UC-NRLF 


\\ 


GIFT   OF 
MICHAEL  REE&E 


J 


— X 


MODERN 
TUNNEL  PRACTICE 


ILLUSTRATED  BY  EXAMPLES 
TAKEN  FROM  ACTUAL  RECENT 
WORK  IN  THE  UNITED  STATES 
AND  IN  FOREIGN  COUNTRIES 


BY 

DAVID   McNEELY   STAUFFER 

r. 

Member  American  Society  of  Civil  Engineers;  Member 

Institution  of  Civil  Engineers;  Vice- President 

Engineering  News  Publishing  Co. 


(i?8  ILLUSTRATIONS) 


NEW   YORK 

ENGINEERING  NEWS  PUBLISHING  CO. 
1906 


Copyright,  1905,  by 
THE  ENGINEERING  NEWS  PUBLISHING  COMPANY 

Entered  at  Stationers'  Hall,  London,  England 
1906 


•"j.:Ft  VALLEY-  CO. 
PRINTERS  AND  BINDERS 
New  York,  U.  S.  A. 


CONTENTS 


PAGE 

PREFACE    vii 

CHAPTER    I 

TUNNEL   LOCATION    AND    SURVEYING 

General  rules  for  location — Geological  considerations — Alignment  of 
tunnels — Station  points — Producing  line  from  portal  into  tunnel — 
Instrumental  work  at  the  Cascade  tunnel — Carrying  center-line 
down  a  shaft — Use  of  electric  light  in  producing  center-line I 

CHAPTER   II 

EXPLOSIVES 

Gunpowder;  its  composition,  reaction,  measure  of  force,  tempera- 
ture, etc. — Nitroglycerine;  its  composition  and  appearance,  action, 
original  method  of  use — Nitro-gelatine,  as  used  in  blasting  opera- 
tions— Dynamite;  its  action,  etc. — Lithofracteur,  Forcite,  Atlas 
powder,  Hercules  powder,  Judson  powder,  Joveite — The  Sprengel 
class  of  explosives — Safety  or  time  fuses — The  primer — Electric 
firing — Cautions  to  be  observed  in  firing  high  explosives — The 
handling  and  storing  of  explosives — Frozen  dynamite  and  its 
treatment — Powder  magazines  14 

CHAPTER  III 

BLASTING 

General  principles  to  be  observed  in  proportioning  depth  and  diameter 
of  holes  to  the  work  to  be  done — The  line  of  least  resistance  in 
blasting — The  location  of  bore-holes — The  square  and  the  V-shaped 
center  cut — The  consumption  of  explosives — Method  pursued  on 
the  New  York  Subway  work — Testing  the  blasting  qualities  of 
rock — Loading  with  black  powder — Loading  with  dynamite — 
Effect  of  nitroglycerine  fumes  and  precautions  to  be  observed — 
Hints  on  power-drilling — Device  for  preventing  the  crushing  of 

shaft-timbers  by  the  flying  rock 34 

iii 


146242 


IV  CONTENTS 

CHAPTER  IV 

NOTES   ON    SHAFT-SINKING 

PAGE 

Location  of  a  shaft — Dimensions — Relation  of  shaft-work  to  tunneling 
proper — General  conditions  of  shaft-sinking — Forces  exerted  and 
precautions  to  be  observed  in  framing — A  steel  shaft-house — 
Cages  and  skips — A  cheap  hoisting-cage  and  head-house — Shaft- 
sinking  in  wet  gravel  and  quicksand — Sheet-piling  shaft 47 

CHAPTER   V  ,4 

PRINCIPLES    OF   TUNNEL   TIMBERING    AND   DRIVING 

General  rules — Choice  of  timber — English  method  of  timbering  as  ap- 
plied in  the  United  States — Belgian  and  Belgian-French  systems — 
German  S3'stem — Austrian  system— American  system— Driving 
through  loose  gravel — Crutch  system — Timbering  a  sand  tunnel — 
Meem  poling-board  system — Iron  crown-bar  system — Old  rail 
crown-bars,  their  advantages  and  disadvantages— Steel-lined  tunnel 
— Sand-chamber  and  caisson  method — Pilot-tunnel  system — 
Sewer  tunnel  in  quicksand — Dry-sand  tunneling — Enlarging  tun- 
nel in  soft  grounds — Sewer  tunnel  in  dry  sand 65 

CHAPTER  VI 

TUNNEL    ARCH    CENTERS 

Requisites  of  a  good  arch  center — Methods  of  framing  centers — Adjust- 
able or  moving  centers — Steel-rib  .centers — Concrete-form  for 
small  tunnels — Placing  concrete  lining  in  tunnels 99 

CHAPTER  VII 

SUB-AQUEOUS    TUNNELS    AND    TUNNEL    SHIELDS 

Form  of  shield  and  methods  pursued  at  East  Boston  Subway — East 
River  gas  tunnel — Massachusetts  pipe  line — Blackwell  tunnel — St. 
Clair  tunnel — Berlin-Spree  tunnel — Harlem  River  tunnel — Penna. 
R.  R.  Hudson  River  tunnel — Screw-jack  shield — Shankland 
shield — Metropolitan  Railway  in  Paris 112 

CHAPTER    VIII 

SUBWAYS,   OR  UNDERGROUND   RAILWAYS 

General  notes  on  location — Orleans  Railway  in  Paris — Boston  Subway 
— East  Boston  tunnel — Buda-Pest  Subway — New  York  Rapid 
Transit  Subway — Atlantic  Avenue  Subway  in  Brooklyn 144 


CONTENTS  V 

CHAPTER  IX 

SPECIAL   TUNNEL-BUILDING    PLANT 

PAGE 

Cascade  tunnel  plant — Scraper-loading — Automatic  dump  at  shafts — 
Dumping-wagon — Cement-mortar  car — Walker's  detaching  hoist- 
hook — Concrete-mixer  I71 

CHAPTER  X 

•        SOME    DATA    UPON    THE    COST    OF    TUNNELING 

Cost  of  hand-drilling  in  shaft-sinking — Cost  of  power-drilling  in  shaft- 
work — Cost  of  drifting  and  cross-cutting — Cost  of  diamond-drill 
work — Cost  of  square-set  mine  timbering — Cost  of  mine  hauling 
by  compressed  air — Cost  of  concrete  tunnel  lining — Cost  of  water- 
hauling  vs.  pumping  in  mines — Cost  of  driving  a  mine-heading — 
Cost  of  tunnel  driving  and  steam-shovel  work 186 

CHAPTER    XI 

THE  VENTILATION  OF  TUNNELS 

The  principles  of  artificial  ventilation — The  Saccardo  system — Ventila- 
tion methods  in  the  Boston  Subway — The  East  Boston  tunnel, 
the  Baltimore  and  Potomac  tunnel,  the  Paris-Orleans  Railway, 
the  Pennsylvania  Avenue  Subway,  the  Simplon  tunnel 201 

CHAPTER    XII 

AIR-LOCKS 

The  general  purpose  of  air-locks — Their  location — The  limits  of  human 
endurance  under  compressed  air — Effect  of  compressed  air  upon 
the  workman — Compressed-air  hospital  locks — The  O'Rourke  air- 
lock— Mirabeau  bridge  air-lock — The  Hughes  air-lock — Hyde  Park 
tunnel  air-lock — Morison  air-lock — Victoria  bridge  air-lock — Air- 
locks at  Kiel  dry-dock 213 

CHAPTER    XIII 

TUNNEL   NOTES 

The  freezing  process  for  shaft-sinking  in  wet  ground — Its  application 
at  Ronnenberg  and  Iron  Mountain — Tunnel  rock  temperatures — 
Definition  of  quicksand— Making  water-tight  concrete— The  hand- 
auger  in  prospecting  work — Tunnel  cross-section  instrument — 
Coxe  plummet  lamp 236 


VI  CONTENTS 

CHAPTER   XIV 

PAGE 

The  construction  of  the  Simplon  tunnel — Water-works  tunnel  at  Cin- 
cinnati, Ohio — Telephone  and  freight  transportation  tunnels  in 
Chicago 250 

APPENDIX 
Glossary  of  some  of  the  more  unusual  terms  used  in  tunneling 301 


PREFACE 

The  practice  of  tunneling,  in  many  of  its  important  features, 
has  been  radically  changed  within  a  comparatively  short  period 
by  the  introduction  of  high  explosives,  by  the  use  of  machine 
drills,  by  special  appliances  for  handling  the  debris  or  pro- 
tecting the  roof  of  the  tunnel,  and  by  the  employment  of  electric 
power  and  light.  As  a  consequence  of  these  innovations,  much 
that  was  useful  to  the  engineer  and  to  the  contractor  in  the 
older  works  upon  tunneling  is  now  out  of  date ;  and  with  this 
in  view,  the  present  work  has  been  compiled. 

As  to  methods  to  be  pursued,  it  is  unnecessary  to  tell 
the  practicing  engineer  that  each  piece  of  tunnel  work  is  prac- 
tically a  problem  calling  for  individual  solution.  No  broad 
rules  can  be  laid  down  which  will  cover  all  possible  conditions, 
though  some  general  principles  for  guidance  can  be  formulated. 
In  the  arrangement  of  this  work,  therefore,  especial  effort  has 
been  made  to  present  modern  practice  in  tunneling  under  as 
many  varying  conditions  as  possible,  and  to  clearly  and  con- 
cisely describe  the  methods  actually  adopted  in  carrying  on  the 
work  under  certain  controlling  conditions. 

The  material  used  is  very  largely  taken  from  the  detailed 
descriptions  of  modern  tunnel  work  as  these  are  found  in  the 
pages  of  technical  journals  and  in  the  proceedings  of  engineer- 
ing societies,  supplementing  this  by  the  personal  experience  of 
engineers  and  contractors  who  do  not  usually  make  a  formal 
record  of  this  experience.  Illustration  is  very  freely  employed, 
because  it  frequently  tells  more  than  can  be  expressed  in  the 
text  alone.  And  in  every  case  the  description  of  any  especial 
method  is  prefaced  by  a  brief  statement  of  the  physical  condi- 
tions which  called  for  some  particular  treatment.  It  is  believed 
that  the  examples  selected  cover  a  wide  range  of  practice.  As 


Vlll  PREFACE 

only  typical  modern  cases  have  been  cited,  no  attempt  has  been 
made  to  include  every  important  tunnel.  The  field  is  too  wide, 
in  fact,  to  be  intelligently  covered  in  any  one  book. 

The  instrumental  work,  or  surveying,  connected  with  tunnel- 
ing, differs  very  little  from  that  common  to  all  larger  public 
works,  and  as  many  special  textbooks  are  devoted  solely  to  the 
use  and  care  of  engineering  instruments,  what  is  here  said  upon 
that  subject  is  intended  simply  as  a  general  statement  of  the 
processes  involved  and  of  their  sequence. 

The  composition,  nature  and  use  of  modern  explosives  have 
been  treated  at  considerable  length ;  but  here  again,  much  has 
been  left  out  that  was  considered  as  having  little  or  no  useful 
bearing  upon  modern  practice  in  tunnel  building. 

The  writer  acknowledges  his  indebtedness  for  some  of  the 
material  here  used,  to  Mr.  Drinker's  monumental  work  upon 
tunneling,  published  in  1878.  And  he  has  also  freely  used  the 
comprehensive  handbook  upon  explosives,  written  by  Mr.  M. 
Eisler,  and  the  excellent  manual  on  the  care  and  handling  of  ex- 
plosives prepared  by  Prof.  Courtenay  De  Kalb,  for  the  Ontario 
Bureau  of  Mines. 

D.  McN.  STAUFFER. 

New  York  City,  Dec.  i,  1905. 


CHAPTER  I 

TUNNEL   LOCATION    AND   SURVEYING 

Selection  of  a  tunnel  route — General  rules  for  location — Geological  con- 
siderations— Alignment  of  tunnels — Station  points — The  Cascade 
tunnel — Carrying  the  center-line  down  a  shaft — Tunnel-targets. 

The  route  selected  for  a  tunnel  depends  somewhat  upon  the 
end  in  view.  If  the  tunnel  is  intended  to  meet  the  demands 
of  modern  rapid-transit  in  a  great  city,  or  if  it  is  proposed  to- 
connect  two  parts  of  a  city  separated  by  a  waterway,  the  lines 
of  traffic  as  indicated  by  existing  streets  will  very  generally 
control  the  location.  In  such  cases  the  engineer  has  a  com- 
paratively narrow  choice  of  routes ;  and  he  must  deal  with  the 
problem  as  he  finds  it. 

Railway  tunnels,  other  than  the  rapid-transit  tunnels  re- 
ferred to,  have  for  their  chief  objects  the  reduction  of  grades 
.and  the  shortening  of  distance  between  given  points  separated 
by  a  dividing  mountain  or  ridge,  or  a  projecting  spur.  In 
such  cases  the  surface  conditions  may  be  so  complex  as  to  ad- 
mit of  several  distinct  tunnel  lines  between  the  terminal  points ; 
and  it  is  the  business  of  the  engineer  to  find  the  one  line  best 
adapted  to  the  proposed  traffic  and  the  most  economical  in  con- 
struction and  operation. 

No  fixed  laws  can  be  laid  down  for  the  engineer  that  will 
cover  every  possible  contingency  of  tunnel  location.  The  ex- 
perience of  the  locating  engineer  in  similar  work  and  his  good 
judgment  as  based  upon  this  experience  can  alone  produce  suc- 
cessful results. 

There  are,  however,  some  general  points  that  must  be  care- 
fully weighed  by  the  engineer  as  these  are  presented  in  his 
study  of  the  actual  topography  of  the  country  to  be  traversed. 

A  tunnel  is  always  an  expensive  and  troublesome  piece  of 


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i.^iO'lijAD, 

2  MODERN    TUNNEL    PRACTICE 

construction;  and  it  should  be  avoided  if  conditions  of  traffic 
and  the  economic  operation  of  this  traffic  will  warrant  any  other 
solution  of  the  problem. 

But  it  should  not  be  forgotten  that  there  are  cases  where  a 
tunnel  is  safer  and  is  really  more  economical  in  the  end  than  an 
apparently  cheaper  open  cut  or  a  longer  and  curved  line  passing 
around  some  natural  obstruction.  In  the  case  of  the  open  cut, 
the  material  may  show  a  tendency  to  slide,  and  the  volume  that 
ultimately  may  have  to  be  removed,  to  provide  a  stable  slope, 
may  be  so  great  as  closely  to  approximate — if  not  exceed — the 
estimated  cost  of  a  tunnel.  On  the  other  hand,  tunneling 
through  ground  of  this  description  is  expensive  work ;  and  the 
utmost  care  and  experience  are  necessary  in  deciding  upon  the 
plan  finally  to  be  adopted.  As  the  necessary  slope  in  the  sides 
o'f  a  cut  can  rarely  be  decided  upon  in  advance,  and  as  this  slope 
is  practically  controlled  by  the  stratification  of  the  ground,  the 
operated  line  in  an  open  cut  is  subjected  to  positive  danger  from 
slides  of  earth  or  rock.  In  elevated  and  mountainous  regions, 
subject  to  heavy  snowfalls  and  resulting  avalanches,  or  falls  of 
rock  loosened  by  frost,  the  open  cut  is  especially  objectionable, 
and  the  more  expensive  tunnel  may  be  advisable,  and  really 
cheaper  in  the  end. 

In  a  winding  valley  with  relatively  sharp  curves  a  tunnel  or 
a  series  of  tunnels  will  usually  reduce  distance  and  permit  of  a 
better  location  and  more  economical  operation  than  a  curved 
surface  line.  And  in  such  cases  it  is  often  good  practice  to 
build  a  tunnel  rather  than  to  erect  and  maintain  the  bridges 
otherwise  necessary  at  stream  crossings.  Careful  surveys  and 
a  close  study  of  alternative  plans  can  alone  decide  these  points. 

In  the  suburbs  of  large  cities  a  tunnel  may,  again,  be  a 
cheaper  structure  than  a  sunken  way,  with  its  many  street 
bridges,  or  than  an  elevated  structure  occupying  valuable  land. 

Geological  Considerations  in  Tunnel  Location — The  cost  of  a 
tunnel  is  largely  measured  by  the  character  of  the  material  pen- 
etrated. A  careful  study  of  the  natural  formation  is  therefore 
a  necessary  preliminary  to  any  intelligent  estimate  of  this  cost, 
or  even  to  any  final  location. 


TUNNEL    LOCATION    AND    SURVEYING  3 

It  is  practically  impossible  to  foretell  with  any  degree  of  cer- 
tainty just  what  material  and  what  stratification  may  be  found 
in  the  interior  of  a  mountain.  And  that  a  geological  forecast 
of  this  kind  should  have  any  value  at  all,  this  work  should  be 
entrusted  only  to  a  geologist  of  wide  experience  and  good  judg- 
ment ;  and  even  then  the  records  of  engineering  are  full  of  the 
mistakes  of  experts  in  this  connection.  In  most  cases  borings 
made  along  the  line  of  the  work  can  alone  be  depended  upon, 
though  these  borings  may  also  deceive  if  read  by  the  inexpert. 

There  are,  however,  surface  indications  that  have  some  value 
in  establishing  the  general  character  of  the  work  to  be  per- 
formed. ,  If  the  rock,  in  its  outcroppings,  is  hard  and  relatively 
little  affected  by  atmospheric  conditions,  it  may  be  classed  as 
good  and  probably  will  stand  well.  If,  on  the  other  hand,  this 
surface  rock  is  seamy,  or  shows  a  tendency  to  disintegrate  under 
the  effect  of  moisture  and  frost,  or  if  it  contains  pyrites,  heavy 
timbering  and  troublesome  and  expensive  work  may  be  ex- 
pected. 

The  general  inclination  of  the  strata,  with  reference  to  the 
tunnel  section,  and  the  frequency  of  seams  in  the  rock,  indicate 
to  some  extent  the  pressures  or  slips  to  be  guarded  against  and 
the  amount  and  kind  of  timbering  necessary.  The  existence  of 
bodies  of  water  lying  above  the  tunnel  level,  taken  jn  connec- 
tion with  any  prevailing  direction  in  the  rock  seams,  affords 
some  indication  of  the  amount  of  water  to  be  dealt  with  and 
the  pressure  with  which  it  will  escape  into  the  workings.  In 
the  case  of  a  deep  and  long  tunnel,  however,  it  is  generally  im- 
possible to  trace  underground  conditions  with  any  degree  of 
certainty;  and  the  safest  course  is  to  generally  guard  against 
the  unexpected. 

Among  the  treacherous  and  difficult  materials  encountered 
in  tunneling  the  following  are  probably  the  worst :  Laminated 
wet  clay  that  may  exert  enormous  pressures  by  swelling:: 
shales  liable  to  swell  and  to  disintegrate  Upon  exposure  to  air  or 
water ;  small,  dry,  loose  sand  or  gravel,  that  will  run.  like  a  fluid 
through  a  relatively  small  opening  and  bring  unequal  pressures 
upon  the  timbering,  and  water-bearing  sand.  Each  one  of  these 


4  MODERN    TUNNEL    PRACTICE 

materials  demands  special  treatment,  expensive  timbering  and 
heavy  masonry  lining,  and  patience.  How  engineers  have  met 
these  problems  in  actual  practice  will  be  seen  in  following 
chapters  of  this  work. 

Tunnel  Surveying. — When  the  general  location  of  a  tunnel 
route  has  been  definitely  fixed,  the  points  to  be  next  considered 
are :  The  exact  alignment,  the  gradients  to  be  adopted,  the  final 
length  of  the  tunnel,  and  the  establishment  of  permanent  sta- 
tions marking  the  line. 

Wherever  possible  the  alignment  should  be  a  tangent.  A 
straight  line  is  the  shortest  line  between  two  points,  and  it  is 
most  easily  and  certainly  carried  through  the  workings.  In 
very  mountainous  regions,  however,  and  especially  where  a 
line  has  to  follow  a  deep  and  crooked  gorge  with  precipitous 
sides,  curvature  in  the  tunnel  or  tunnels  may  be  absolutely  un- 
avoidable. And  in  great  tunnels,  like  the  St.  Gothard,  for  ex- 
ample, spiral  and  looped  tunnels  are  employed  for  the  purpose 
of  obtaining  distance  and  consequently  easier  grades,  in  a  line 
run  between  two  points  that  are  horizontally  near  each  other, 
but  vary  greatly  in  relative  elevations. 

Unless  the  grade  is  a  continuous  one,  which  is  rarely  the  case, 
the  summit  or  highest  point  in  the  tunnel  should  be  as  near  to 
the  center  of  the  tunnel  as  possible.  By  this  disposition  of  the 
summit  natural  drainage  is  secured  toward  the  two  portals. 
Except  in  very  long  tunnels,  or  in  tunnels  having  a  compara- 
tively small  depth  of  ground  overlying  them,  intermediate 
shafts  have  been  largely  eliminated  by  the  introduction  of  high 
explosives  and  modern  machinery,  which  vastly  shorten  the 
time  of  completion  and  do  away  with  the  necessity  of  increas- 
ing the  number  of  working  faces  by  multiplying  shafts.  This 
absence  of  shafts  has  a  direct  effect  upon  the  drainage  problem 
and  decreases  pumping. 

The  final  length  of  a  tunnel  is  generally  fixed  by  the  most 
economical  limits  of  the  open-cut  approaches;  and  this  length 
cannot  be  definitely  known  until  the  approaches  are  actually 
completed. 

The  instrumental  work  of  a  tunnel  survey  is  largely  that  of 


TUNNEL    LOCATION    AND    SURVEYING  5 

any  other  important  survey ;  the  chief  requisites  being  first-class 
instruments  and  experience,  care  and  patience  on  the  part  of  the 
observers. 

Assuming  that  the  line  is  a  tangent,  the  problem  to  be  solved 
is  the  laying  down  of  this  line  across  the  mountain  to  be  pierced, 
extending  this  line  beyond  both  portals  and  then  permanently 
marking  the  established  line  in  such  manner  that  it  can  be  pro- 
duced into  each  portal.  If  the  tunnel  is  surmounted  by  a  single 
peak  or  ridge,  from  which  both  ends  of  the  tunnel  can.  be  seen, 
the  problem  is  presented  in  its  simplest  form.  The  preliminary 
line,  or  a  special  survey,  will  approximately  fix  the  summit 
point;  but  this  point  must  then  be  tested  and  adjusted  by  a 
patient  series  of  sights  and  reversed  sights  taken  upon  stations 
assumed  to  mark  the  ends  of  the  line,  and  the  necessary  shifting 
laterally  of  the  transit  instrument.  With  the  mean  of  many 
sights  finally  adopted  as  indicating  the  correct  line,  a  perma- 
nent sighting  station  is  fixed  upon  this  summit  which  serves 
as  a  forward  sight  for  each  portal  station,  in  prolonging  the  line 
into  the  tunnel  as  work  progresses. 

If  the  tunnel  is  very  long,  or  the  summit  of  the  mountain  is 
broken  into  several  ridges  and  the  ends  of  the  tunnel  cannot  be 
seen  from  a  single  middle  station,  then  triangulation  becomes 
necessary,  with  all  the  skill  and  careful  work  that  this  process 
implies.  For  shorter  tunnels  any  standard  work  on  surveying 
will  indicate  the  triangulation  methods  employed;  and  for  the 
greater  tunnels,  like  those  penetrating  the  Alps,  the  reader  is 
referred  to  the  history  of  these  tunnels. 

In  whatever  manner  the  main  station  points  have  been  es- 
tablished, they  must  be  repeatedly  and  carefully  tested  under 
all  atmospheric  conditions;  in  winter  and  in  summer,  and  by 
day  and  by  night.  Experience  proves  that  the  best  time  for 
sighting  is  about  sunrise,  before  the  heat  of  the  sun  can  cause 
atmospheric  disturbances.  A  plummet-lamp,  used  on  a  clear, 
calm  night,  is*  usually  found  to  give  more  accurate  results  than 
other  forms  of  targets  sighted  upon  in  the  daytime. 

The  permanent  station  points  should  be  very  solidly  con- 
structed, with  stone  foundations  laid  deep  enough  to  be  unaf- 


6  MODERN    TUNNEL    PRACTICE 

fected  by  frost.  And  in  the  case  of  the  summit  station,  sighting 
conditions  may  demand  that  the  line  point  be  transferred  to  the 
top  of  a  strong  and  rigidly  braced  wooden  structure,  sur- 
mounted by  a  platform  about  8  feet  square. 

Especial  care  must  be  exercised  in  locating  and  in  preserving 
the  portal  stations  from  all  danger  of  interference;  for  it  is 
from  these  stations  that  the  line  is  prolonged  into  the  tunnel. 
AVorkmen  are  proverbially  careless  in  the  matter  of  preserving 
"points,"  either  inside  or  outside  of  the  tunnel,  and  it  remains 
to  the  engineer  to  devise  means  of  minimizing  danger  in  this 
connection. 

To  diminish  some  of  the  difficulties  encountered  in  preserv- 


FlG.   I.— Dunham  Method  of  Tunnel  Alignment. 

ing  the  tunnel  points,  Mr.  H.  F.  Dunham,  M.  Am.  Soc.  C.  E., 
suggests  the  following  mode  of  procedure.*  In  the  first  place, 
he  removes  his  line  from  the  center  of  the  tunnel  approach, 
where  it  is  always  in  trouble,  to  one  side  of  this  approach.  At  a 
point  about  50  feet  from  the  tunnel  portal,  and  against  one  side 
of  the  approach,  he  built  a  strong  timber  platform,  supported  by 
8  x  12-inch  posts  set  3  feet  into  the  rock.  As  the  alignment 

"Trans.  Am.  Soc.  C.  E.;  Vol.  XXVII,  p.  453. 


TUNNEL    LOCATION    AND    SURVEYING  / 

of  a  timbered  tunnel  is  generally  established  by  the  lining-up 
of  the  wall-plates,  the  level  of  this  platform  was  such  that  when 
an  ordinary  wye-level  was  set  upon  it  the  line  of  sight  would 
strike  a  little  above  and  inside  the  line  of  the  wall-plates  on 
that  side  of  the  tunnel.  To  enable  the  instrument  to  be  quickly 
set  in  position  small  holes  were  made  in  the  platform  and-pro- 
tected  by  iron  washers,  marking  the  position  of  the  three  legs. 

The  distance  between  the  center-line  of  the  tunnel  and  the 
center-line  of  the  instrument  and  the  height  of  the  instrument 
were  carefully  measured  and  noted;  and  these  measurements 
were  used  in  fixing  a  permanent  target  back  of  the  portal  and 
about  1,000  feet  away.  A  gage-board  of  convenient  form  was 
then  made,  which  would  rest  upon  the  corner  of  the  wall-plate 
and  also  support  a  plummet-lamp.  A  larger  board  was  pro- 
vided that  would  span  one-half  the  distance  between  the  wall- 
plates;  and  in  both  gages  the  parts  liable  to  wear  were  pro- 
tected with  iron. 

The  work  of  alignment  was  then  conducted  as  follows :  The 
instrument  was  set  upon  the  platform,  sighted  upon  the  rear 
target,  and  securely  clamped.  The  level  was  next  carefully  re- 
versed in  the  wyes  and  used  to  line-in  the  plummet-lamp  at- 
tached to  the  smaller  gage-board,  this  board  being  held  upon 
the  wall-plate  and  the  plate  moved  laterally,  or  raised  and  low- 
ered, as  the  rodman  might  direct.  With  the  wall-plate  on  one 
side  of  the  tunnel  fixed  in  place,  the  longer  gage,  with  a  spirit- 
level  placed  upon  it,  was  employed  in  determining  the  posi- 
tion of  the  opposite  wall-plate.  To  carry  out  this  method  a 
space  2  feet  wide  and  2  feet  high  must  be  kept  cleared  of  all 
timber  and  broken  stone  across  the  floor  of  the  heading. 

Mr.  Dunham,  in  describing  this  method,  says  that  the  neces- 
sary instrumental  work  can  be  done  in  one-fourth  the  time  de- 
manded in  the  older  methods.  The  work  performed  by  the 
level  was  checked  up  at  intervals  by  running-in  the  center  line 
with  a  transit.  Under  conditions  under  which  men  could  work, 
the  plummet-lamp  could  be  sighted  upon  up  to  about  1,000 
feet. 

The    Cascade    Tunnel. — The    following    account    of    instru- 


8 


MODERN    TUNNEL    PRACTICE 


mental  work  done  at  the  Cascade  tunnel  of  the  Great  Northern 
Railway  is  condensed  from  an  article  written  by  the  then  chief 
engineer,  John  F.  Stevens,  M.  Am.  Soc.  C.  E.,*  now  chief  en- 
gineer of  the  Panama  Canal.  As  shown  by  the  map  presented, 
we  here  have  in  concrete  form  the  economic  gain  of  a  tunnel 
over  surface  crossing  of  this  same  mountain,  the  surface  line 
in  this  case,  however,  being  represented  by  a  temporary  switch- 
back used  during  the  construction  of  the  tunnel.  This  switch- 
back represents  the  cheapest  location  across  the  ridge.  To  have 
flattened  out  the  curves  and  to  have  reduced  the  gradients  by 


FIG.   2. — Map,    Showing   Cascade   Tunnel   Location    and   the   Temporary 

Switchback. 

the  necessary  loops  would  have  made  the  contrast  still  more 
striking  between,  the  surface  and  the  tunnel  lines. 

As  compared  with  the  switchback,  the  construction  of  the 
tunnel  saved  9  miles  in  distance,  2,332°  of  curvature,  and 
700  feet  in  rise  and  fall.  Aside  from  these  considerations  of 
construction  and  decrease  in  time  of  crossing  the  summit,  the 
building  of  this  straight  tunnel  vastly  decreased  the  mainte- 
nance-of-way  expenses.  Mr.  Stevens  points  out  that  the  snow- 
fall in  the  Cascade  Range  is  excessive,  and  in  the  winter  of 
1897-98  the  aggregate  snowfall  at  the  summit  of  the  switch- 

*Engincering  News,  Jan.  10,  1901. 


TUNNEL    LOCATION    AND    SURVEYING  Q 

back  was  140  feet,  with  20  feet  of  snow  on  the  level  at  times. 
The  removal  of  this  snow  from  the  switchback  tracks  was  very 
difficult  and  costly;  and  this  factor  of  expense,  and  also  the 
delay  in  traffic,  were  the  determining  factors  in  deciding  upon 
the  tunnel  line. 

The  accompanying  map  shows  that  the  mountain  overlying 
the  tunnel  line  has  two  peaks,  the  western  or  highest  peak  hav- 
ing an  elevation  of  2,150  feet  above  the  portal  at  that  end,  and 
the  eastern  peak  lying  1,750  feet  above  the  east  portal.  By 
many  trials  transit  points  were  established  on  each  of  these 
peaks,  each  commanding  the  other,  as  well  as  points  just  out- 
side the  two  portals.  These  points  were  carefully  checked  by 
observations,  repeated  many  times  under  the  most  favorable 
atmospheric  conditions. 

Timber  towers  16  feet  high  were  erected  at  each  of  these 
summit  stations,  and  in  the  center  of  each  tower  gas-pipe  tar- 
gets were  secured ;  each  pipe  was  2  inches  in  diameter  and  20 
feet  long,  so  as  to  be  seen  above  the  deep  snow ;  and  whenever 
the  opportunity  offered  these  pipe  targets  were  tested  by  drop- 
ping a  plumb-line  through  them  to  a  tack  below  them.  Inter- 
mediate fore-sights  were  also  located  on  the  mountainside,  to 
be  used  when  the  summit  targets  were  obscured  by  clouds.  At 
each  portal  permanent  transit  stations  were  made  by  building 
a  strong  elevated  structure,  spanning  the  working  tracks  and 
roofed  over. 

The  length  of  the  tunnel  was  obtained  by  direct  measure- 
ments, this  method  being  preferred  to  any  system  of  triangu- 
lation  possible  on  that  ground.  Measurements  were  made  with 
a  400- foot  steel  tape,  on  measurement  points  previously 
established  as  nearly  400  feet  apart  as  the  nature  of 
the  ground  would  permit.  These  "points"  were  located  on 
high  stumps,  on  braces  nailed  to  trees,  or  on  plugs  driven  into 
holes  drilled  in  the  rock;  the  elevations  of  these  points  were 
carefully  taken  with  the  level.  In  measuring,  the  tension  of  the 
steel  tape  was  regulated  by  a  spring  balance,  and  the  tempera- 
ture was  noted  at  each  end  of  the  steel  tape.  Work  was  usu- 
ally done  on  cloudy  days  and  when  there  was  little  wind ;  and 


TO  MODERN    TUNNEL    PRACTICE 

as  a  preliminary  a  base-line  had  been  laid  out  with  a  loo-foot 
standard  tape,  and  with  this  the  proper  tension  to  apply  to  the 
400- foot  tape  was  fixed,  62°  Fahr.  being  assumed  as  the  nor- 
mal temperature.  From  the  slope  measurements,  corrected  for 
temperature  and  vertical  measurements,  the  horizontal  dis- 
tances were  calculated. 

Inside  the  tunnel  the  measurements  were  carried  along-  the 
plumb-posts,  and  after  the  concrete  lining  had  been  completed 
each  station  was  marked  on  plugs  driven  into  holes  drilled  in 
the  concrete.  Bench-marks  for  the  levelman  were  made  in  a 
similar  manner. 

In  prolonging  the  center-line,  transit  sights  were  placed  in 
the  key-segment  of  the  timber  arch ;  and  at  intervals  of  about 
800  feet  platforms  were  erected  at  the  elevation,  of  the  wall- 
plates,  with  two  independent  floors,  one  to  support  the  transit, 
and  the  other  to  hold  the  observer.  Electric  lights,  carefully  cen- 
tered, served  as  back-sights.  By  this  arrangement  of  transit 
platforms  the  muck  and  concrete  cars  passed  beneath  them 
without  interfering  with  the  work  of  the  engineering  party. 

Carrying  a  Center-line  Down  a  Shaft. — While  modern  methods 
of  tunnel-driving  have  eliminated  shaft-work  to  a  considerabl  e 
extent,  it  is  still  necessary  at  times  to  transfer  the  center-line  of 
a  tunnel  down  a  shaft,  the  difficulties  of  the  problem  increasing 
with  the  depth  of  the  shaft. 

To  do  this  the  center-line  must  be  carried  to  the  mouth  of 
the  shaft,  and  marked  upon  permanent  station-points  located 
on  either  side  of  the  shaft  and  about  25  feet  away  from  the 
shaft.  While  the  shaft  timbers  themselves  may  now  be  used 
for  the  prolongation  of  the  center-line,  it  is  better  to  place 
these  marks  on  solid  supports  near  to,  but  independent  of  the 
shaft  lining.  With  these  shaft  points  fixed,  two  horizontal  steel 
wires,  about  one-sixteenth  inch  apart,  are  stretched  between 
the  points,  with  the  space  between  the  wires  coinciding  with 
the  center-line.  These  steel  wires  are  usually  kept  tightly 
stretched  by  means  of  a  small  drum  and  ratchet. 

To  transfer  to  the  bottom  the  line  thus  established  over  the 
mouth  of  the  shaft,  two  wires  of  steel  or  copper,  strong  and  as 


TUNNEL    LOCATION    AND    SURVEYING  II 

small  as  possible,  are  passed  between  the  horizontal  wires  and 
as  far  apart  as  the  dimensions  of  the  shaft  will  permit.  To 
the  bottom  of  these  wires  two  plummets,  weighing  15  pounds 
or  more,  are  attached.  If  the  shaft  is  deep  the  suspended  wires 
are  liable  to  disturbance  by  air  currents,  or  by  falling  water, 
and  in  such  cases  the  wires  are  often  protected  by  passing  them 
through  light  pine  boxes,  about  6  inches  square,  attached  to  the 
floor  of  the  shaft.  To  check  oscillation  in  the  plummet-wires 
the  plummets  themselves  are  allowed  to  swing  in  buckets  of 
water,  oil,  or  some  other  fluid,  placed  in  the  bottom  of  the  shaft. 

The  final  operation  is  to  determine,  from  the  position  of  the 
two  plummet-wires  at  the  bottom  of  the  shaft,  the  correct  cen- 
ter-line ;  to  permanently  mark  this  center-line  at  the  bottom,  and 
to  prolong  this  line  into  the  tunnel  in  both  directions  as  the 
headings  progress.  As  the  base-line  thus  transferred  is  neces- 
sarily very  short,  an  exceedingly  small  error  is  rapidly  multi- 
plied in  the  prolongation,  and  the  utmost  care  and  patience  must 
be  observed  throughout. 

To  fix  the  line  below,  two  beams  are  securely  fastened  just 
above  the  roof  of  the  tunnel  and  close  to  the  two  plummet- 
wires.  To  these  beams  brass  scales  are  attached,  and  the  oscil- 
lation of  the  wires  before  these  scales  is  patiently  watched  and 
noted.  The  mean  of  hundreds  of  these  oscillations  is  finally 
assumed  as  marking  the  true  line,  and  this  mean  is  marked 
upon  the  scales.  From  these  latter  marks  two  other  plummets 
are  suspended,  and  from  these  thin  wires  the  tunnel  line  is  pro- 
longed by  a  transit,  in  the  usual  manner  of  shifting  and  check- 
ing. If  the  tunnel  has  a  firm  rock  roof,  the  line  of  prolonga- 
tion is  marked  by  driving  plugs  into  holes  drilled  in  the  roof, 
and  from  small  hooks  in  these  plugs  plummet-lamps  are  sus- 
pended for  sights. 

The  device  shown  in  Fig.  3  is  the  scale  used  in  marking  the 
center-line  at  the  bottom  of  the  shaft  on  the  Central  Park  tun- 
nel of  the  New  York  Rapid  Transit  Railway.  In  this  case 
the  distance  between  the  wires  was  only  7.9  feet ;  and  fine  piano 
wire  was  used  for  suspending  25-pound  plummets,  hanging 
freely  in  a  tub  of  water.  The  brass  bars  were  fixed  in  the 


12  MODERN    TUNNEL    PRACTICE 

roof  as  shown,  and  the  center  part  was  graduated  in  tenths  and 
hundredths  of  a  foot.  A  vernier,  reading  to  two-thousandths, 
slides  over  the  top  of  the  bar,  with  its  zero  intersected  by  the 
plummet-line. 

One  of  the  most  notable  cases  of  alignment  transfer  down 
a  deep  shaft  is  the  work  of  this  class  done  at  the  Hoosac  tunnel. 
This  shaft  was  1,030  feet  deep,  and  it  was  encumbered  by 
sixty-four  separate  floors.  The  base  available  at  the  bottom  of 
the  shaft  was  23  feet  long,  and  to  this  the  line  was  transferred 
from  the  surface  practically  in  the  manner  described  above. 
But  from  this  base  of  23  feet  the  engineers  prolonged  the  cen- 


i      ,       '-Graduation 
\J  Divided  Into  Tenths 

of  Inches 

CM.  \Plumb  .- 

"*•*•  I    Un»  Line 


El«votlon.  Cross    Section. 

FIGt  3_Device  Used  for  Marking  the   Center-line  of  a  Tunnel,   at  the 

Foot  of  a  Shaft. 


ter-line  1,563  feet  east  and  2,056  feet  west,  with  errors  of  align- 
ment-of  only  5-16  inch  and  9-16  inch  respectively. 

In  this  Hoosac  tunnel  the  ordinary  distant  target  was  a  dark- 
lantern  with  a  small  parabolic  reflector  and  a  panel  of  ground 
glass  on  the  side  facing  the  transit.  In  front  of  this  panel  the 
plummet  was  hung,  this  being  sometimes  a  ^-inch  turned,  black 
rod  forming  part  of  the  suspending  line.  At  other  times  a 
brass  plate  was  employed;  this  plate  was  4  inches  wide,  and 
had  in  it  a  vertical  slit  from  J  to  J  inch  wide,  the  slit  coinciding 
with  the  plumb-line.  With  good  air  in  the  tunnel  these  sights 
were  plainly  seen  at  distances  of  1,000  to  1,500  feet. 

At  the  present  time  electric  lights  are  largely  used  in  tun- 
nels for  sighting  purposes,  and  this  light  is  so  penetrating  that 


TUNNEL    LOCATION    AND    SURVEYING  13 

it  can  be  successfully  used,  even  under  somewhat  foggy  condi- 
tions. Kerosene  lamps,  which  are  easily  handled  by  unskilled 
labor,  also  furnish  excellent  results;  and  in  geodetic  work  an 
8-inch  reflector  attached  to  a  lamp  of  this  kind  enabled  the  light 
to  be  bisected  at  a  distance  of  forty  miles. 


CHAPTER     II 

EXPLOSIVES 

Gunpowder;  its  composition,  reaction,  measure  of  force,  temperature,  etc. 
— Nitro-glycerine ;  its  composition,  action,  and  original  method  of 
use — Nitro-gelatine,  as  employed  in  blasting  operations — Dynamite ; 
its  action,  etc. — Lithofracteur,  Forcite,  Atlas  powder,  Hercules  pow- 
der, Judson  powder,  Joveite — The  Sprengel  class  of  explosives — Safety 
or  time  fuses — The  primer — Electric  firing — Cautions  to  be  observed  in 
firing  high  explosives — The  handling  and  storing  of  explosives — Frozen 
dynamite  and  its  treatment — Powder  magazines. 

A  variety  of  explosive  compounds  are  now  employed  in  blast- 
ing operations,  though  the  so-called  modern  high  explosives 
have  largely  supplanted  the  old  black  powder  for  all  tunneling 
work.  But  for  purpose  of  information,  the  various  explos- 
ive agents  coming  within  the  scope  of  this  work  are  here  briefly 
described. 

Gunpowder. — This  oldest  of  explosives  is  made  of  various 
percentages  of  nitre,  sulphur  and  charcoal,  according  to  the 
purpose  intended.  For  military  use,  the  proportions  adopted 
by  the  War  Department  of  the  United  States  are:  75  parts 
nitre,  10  parts  sulphur,  and  15  parts  charcoal.  But,  while  this 
is  the  standard  composition,  for  certain  blasting  operations,  as 
in  coal  mining — where  a  heaving,  or  rending,  rather  than  a 
shattering  effect  is  desirable — a  weaker  composition  is  fre- 
quently employed,  the  proportions  being  as  low  as  65  parts 
nitre,  15  parts  sulphur,  and  20  parts  charcoal. 

Good  gunpowder  should  show  hard,  angular  grains  which 
do  not  soil  the  fingers,  and  the  grains  should  have  a  perfectly 
uniform  dark-gray  color.  If  the  color  is  bluish  or  jet-black,  the 
powder  contains  an  excess  either  of  charcoal  or  of  water.  The 
appearance  of  bluish-white  specks  indicates  that  the  nitre  has 
effervesced  in  drying,  or  that  the  powder  has  absorbed  suffi- 

14 


EXPLOSIVES  15 

cient  water  to  partially  dissolve  the  nitre.  In  either  case  the 
mixture  is  no  longer  uniform.  When  gunpowder  is  new  it 
should  be  free  from  dust,  and  it  should  leave  no  residuum  or 
stain  when  flashed  on  a  copper  or  porcelain  plate. 

Probably  the  best  summary  of  the  results  of  the  primary  and 
secondary  reactions  that  occur  in  the  explosion  of  gunpowder 
is  that  given  by  Dr.  Debus,  as  follows  : 

"The  combustion  of  gunpowder  consists  of  two  distinct  stages :  a  pro- 
cess of  oxidation,  which  is  finished  in  a  very  short  time,  occupying  only 
a  very  small  fraction  of  a  second,  and  causing  the  explosion,  and  during 
which  potassium  carbonate  and  sulphate,  carbonic  acid,  and  some  car- 
bonic oxide  and  nitrogen  are  produced ;  and  a  process  of  reduction,  which 
succeeds  the  process  of  oxidation  and  requires  a  comparatively  long  time 
for  its  completion. 

"As  the  oxygen  of  the  saltpeter  is  not  sufficient  to  oxidize  all 
the  carbon  to  carbonic  acid,  and  all  the  sulphur  to  sul- 
phuric acid,  a  portion  of  the  carbon  and  a  portion  of  the  sul- 
phur are  left  free  at  the  end  of  the  process  of  oxidation.  The  carbon  so 
left  reduces,  during  the  second  stage  of  the  combustion,  potassic  sulphate, 
and  the  free  sulphur  decomposes  potassic  carbonate.  Hydrogen  and  marsh- 
gas,  which  are  formed  by  the  action  of  heat  upon  charcoal,  likewise  re- 
duce potassic  sulphate,  and  some  hydrogen  combines  with  sulphur  and 
forms  sulphureted  hydrogen."' 

The  force  of  the  blasting  powder  is  measured  either  by  the 
pressure  of  the  gases  given  off  or  by  the  work  done.  The 
pressure  of  the  gases  depends  upon  the  nature,  volume  and 
temperature;  while  the  work  performed  depends  upon  the 
amount  of  heat  given  off.  It  is  practically  impossible,  however, 
to  exactly  determine  the  potential  energy  of  the  explosion  of 
gunpowder,  owing  to  the  fact  that  its  rate  of  explosion  is  slow 
as  compared  with  modern  compounds ;  and  as  nearly  all  rock  is 
more  or  less  seamy  or  loose,  the  gas  escapes  at  every  crack,  and 
with  this  gas  we  also  lose  heat  that  would  otherwise  perform 
work. 

For  these  reasons  the  force  resulting  from  the  explosion  of 
gunpowder  cannot  be  even  closely  determined.  Various  au- 
thorities figure  it  from  15,000  pounds  per  square  inch  in  loose 
rock,  to  about  200,000  pounds  per  square  inch  in  the  case  of  a 
modern  type  of  gun,  carefully  loaded  with  the  best  and  strong- 
est powder. 


1 6  MODERN    TUNNEL    PRACTICE 

Sir  Frederick  A.  Abel  is  quoted  as  stating  that  gunpowder 
yields  upon  explosion  43%  by  weight  of  permanent  gases,  and 
57%  of  matter  which  is  solid  at  ordinary  temperatures;  but 
part  of  the  latter  may  exist  as  vapor  when  the  powder  is  ex- 
ploded under  pressure.  At  o°  Cent.,  and  ordinary  barometric 
pressure,  the  permanent  gases  generated  by  gunpowder  occupy 
about  280  times  the  volume  of  the  original  powder.  The  tem- 
perature of  the  explosion  is  about  2,000°  Cent.,  and  these  gases 
consequently  exert  a  pressure,  when  developed  in  a  confined 
space,  which  amounts  to  6,400  atmospheres,  or  about  42 
tons  per  square  inch,  if  the  powder  completely  fills  the  space 
in  which  it  is  exploded.  Sir  Frederick  concludes  that  the 
total  theoretic  work  which  gunpowder  is  capable  of  performing, 
in  expanding  indefinitely,  is  about  486  foot-tons  per  pound  of 
powder. 

Nitroglycerine. — Nitroglycerine  was  discovered  by  Sobrero, 
in  1847,  and>  generally  speaking,  it  is  the  product  of  the  action 
of  concentrated  nitric  acid  upon  glycerine,  though  the  processes 
of  manufacture  vary. 

At  ordinary  temperatures  nitroglycerine  is  an  oily  liquid, 
clear  and  colorless,  or  yellowish ;  it  refracts  light,  has  a  sweet- 
ish and  burning  taste,  is  without  odor,  and  has  a  specific  grav- 
ity of  1.6.  At  lower  temperatures  it  becomes  solid.  It  is  in- 
soluble in  water,  but  dissolves  easily  in  ether,  wood  spirit,  ben- 
zol, chloroform,  and  hot  alcohol.  When  taken  into  the  human 
system  it  causes  vertigo,  weakening  of  sight,  stupor,  and  pains 
in  the  cardiac  region;  and  in  larger  doses  it  acts  like  strych- 
nine, over  ten  grains  being  fatal.  Even  mere  contact  with  the 
skin  produces  serious  symptoms,  though  workmen  get  used  to 
it  in  time. 

Pure  nitroglycerine  does  not  decompose  spontaneously  at 
ordinary  temperatures;  it  may  be  gradually  heated  to  100° 
Cent,  without  explosion,  but  it  is  then  very  sensitive  to  slight 
shocks.  At  185°  Cent.,  Champion  says  that 'it  evaporates,  boil- 
ing and  evolving  red  fumes ;  at  217°  Cent,  it  burns  briskly,  and 
at  257°  Cent,  it  detonates  with  violence. 

Alfred  Nobel,  the  discoverer  of  dynamite,  figures  that  one 


EXPLOSIVES  17 

volume  of  nitroglycerine  disengages  1,298  volumes  01  gas  at 
100°  Cent,  at  ordinary  barometric  pressure;  Dr.  List  estimates 
the  bulk  of  the  liberated  gas  at  1,505  volumes.  At  the  lowest 
estimate,  however,  nitroglycerine  evolves  nearly  six  times  as 
much  gas  as  gunpowder  at  100°  Cent.  But,  as  a  far  higher 
degree  of  heat  is  produced  by  the  instantaneous  combustion-of 
nitroglycerine,  Nobel  claims  that  this  heat  expands  the  bulk 
of  the  free  gases  to  eight  times  the  original  1,298  volumes, 
while  the  gas  of  gunpowder  would  not  be  trebled  at  the  same 
temperature.  According  to  volume,  then,  the  explosive  force 
of  nitroglycerine  compares  with  that  of  gunpowder  as  thirteeen 
to  one. 

Nitroglycerine  cannot  be  detonated  by  the  simple  application 
to  it  of  a  flame  or  heated  iron ;  in  a  thin  sheet  the  liquid  simply 
burns  away  like  gunpowder.  It  is  only  when  heated  to  257° 
Cent,  in  a  closed  space,  that  the  entire  mass  explodes.  A  sud- 
den blow  will  evolve  heat  enough  to  explode  it ;  but  in  this  case 
only  the  portion  of  the  liquid  actually  struck  will  detonate.  If 
the  nitroglycerine  is  frozen,  however,  a  blow  given,  to  a  part 
of  the  mass  is  at  once  transmitted  to  the  remaining  portion,  and 
accidents  occur  from  this  cause.  The  sun's  rays  also  transform 
nitroglycerine  into  a  very  unstable,  easily  exploded  substance. 

In  practice,  nitroglycerine  is  exploded  by  the  detonation  of 
an  adjacent  volume  of  gunpowder,  guncotton,  or  fulminates; 
and  this  occurs  whether  the  nitroglycerine  is  loose  or  under 
confinement. 

As  at  first  used  in  blasting  operations,  nitroglycerine  was 
employed  in  conjunction  with  gunpowder.  A  tin  cartridge  tube 
was  filled  first  with  gunpowder,  and  then  nitroglycerine  was 
poured  in.  The  tube  was  closed  by  a  cork  and  placed  in  a  bore- 
hole, made  somewhat  larger  in  diameter  than  the  cartridge, 
and  the  annular  space  was  filled  with  a  coarse-grained  gun- 
powder, which  covered  the  cartridge  about  one  inch  in  depth. 
A  fuse  was  inserted,  the  bore-hole  was  tamped  with  sand,  and 
then  fired.  Nobel,  later,  poured  the  nitroglycerine  directly  into 
the  bore-hole,  and  exploded  it  by  a  special  black-powder  de- 
tonator and  a  fuse. 


!g  MODERN    TUNNEL    PRACTICE 

The  efficiency  of  the  new  explosive  was  at  once  recognized, 
and  a  great  demand  for  it  arose.  But  the  liquid  explosive 
leaked  away  into  seams,  parts  did  not  explode  and  lay  hidden 
in  pockets,  that  were  later  liable  to  detonation  under  the  action 
of  a  drill.  Many  fatal  accidents  occurred,  and  the  blowing 
up  of  ships  at  Colon  and  San  Francisco,  about  1866,  stopped 
the  transport  of  the  new  explosive.  Attempts  were  made  to 
render  nitroglycerine  non-explosive  by  adding  methylic  alcohol, 
that  could  be  removed  by  shaking  in  water ;  but  the  invention 
of  dynamite,  a  comparatively  solid  form  of  nitroglycerine, 
caused  the  liquid  compound  to  be  abandoned  except  for  some 
special  use,  as  in  increasing  the  flow  of  sluggish  oil  wells,  etc. 

Nitrogelatine. — The  first  marked  improvement  on  the  liquid 
form  of  nitroglycerine  was  the  invention,  by  Nobel,  of  nitrogel- 
atine,  or  nitroglycerine  solidified  by  means  of  guncotton  collo- 
dion. This  compound  was  a  solid  jelly,  and  its  inventor  claimed 
that  it  was  very  safe  and  highly  suitable  for  every  purpose  to 
which  a  very  powerful  explosive  could  be  applied.  This  explo- 
sive jelly  was  pressed  into  cartridges,  and  exploded  either  by  a 
strong  fuse  or,  preferably,  by  a  powerful  detonator  charged 
with  fulminate. 

As  described  by  Gen.  Abbot,  nitrogelatine  No.  i,  or  blasting 
gelatine,  contained  92%  nitroglycerine  and  8%  nitro-cotton. 
It  is  straw-colored,  quite  elastic  to  the  touch,  has  a  density  of 
1.6,  and  it  can  be  cut  with  a  knife.  It  softens  a  little  at  a  tem- 
perature of  122°  to  J4O°  Fahr.,  and  when  inflamed  in  the  open 
it  burns  like  dynamite,  or  dry  compressed  guncotton.  Pure 
explosive  gelatine,  slowly  heated,  detonates  at  400°  Fahr. 
When  mixed  with  4  to  10%  of  camphor  it  simply  burns  with- 
out exploding  at  570°  to  600°  Fahr.,  or  the  temperature  at 
which  gunpowder  explodes. 

Nitrogelatine  was  one  time  quite  extensively  used  in  blast- 
ing rock  under  water,  and  is  still  useful  in  military  operations. 

Dynamite. — In  attempting  to  render  nitroglycerine  less  dan- 
gerous and  better  adapted  to  the  uses  of  the  engineer,  Alfred 
Nobel  finally  invented  dynamite.  This  is  simply  a  combination 
of  nitroglycerine  with  some  porous  and  more  or  less  inert  sub- 


EXPLOSIVES  IQ 

stance  that  will  absorb  and  hold  the  liquid  without  leakage. 
Many  materials  were  tried  before  Nobel  adopted  for  this  pur- 
pose kieselguhr,  an  infusorial  earth,  chiefly  found  in  Hanover, 
and  made  up  of  very  minute  siliceous  plant  skeletons,  that  hold 
the  liquid  within  their  recesses.  The  great  success  attending 
the  employment  of  this  kieselguhr  dynamite  led  to  the  inven- 
tion of  a  number  of  nitroglycerine  compounds,  all  having  for 
their  main  purpose  the  substitution  of  the  solid  for  the  liquid 
form,  and  some  adding  other  ingredients  intended  to  render 
the  compound  either  more  powerful  or  safer. 

The  action  and  effect  of  dynamite  proper  are  practically 
stated  under  the  head  of  Nitroglycerine.  Mr.  M.  Eissler,  in 
his  "Handbook  on  Modern  Explosives,"  gives  a  useful  table 
comparing  the  power  which  various  explosives  are  capable  of 
exercising,  bulk  for  bulk.  This  table  is  of  far  greater  import- 
ance in  its  application  to  blasting  than  any  comparison  of  the 
relative  power  of  explosive  substances,  weight  for  weight,  and 
is  as  follows : 

Power  of  Explosives,  Bulk  for  Bulk. — 

Nitroglycerine 100.0 

Ammonia  powder 80.0 

Dynamite,  No.  I,  75%  nitroglycerine 74.0 

Lithofracteur 53.0 

Guncotton    60.0 

Lithofracteur. — This  compound  is  made  of  55%  nitroglycer- 
ine, 21%  kieselguhr,  6%  charcoal,  15%  barium  nitrate  and 
carbonate  of  soda,  or  either  of  them,  and  3%  sulphur  and  man- 
ganese oxide,  or  either  of  them. 

Forcite. — Forcite  was  invented  by  Capt.  J.  M.  Lewin,  of  the 
Swedish  army.  It  is  a  mixture  of  nitroglycerine  with  cellu- 
lose, the  latter  being  gelatinized  by  heating  in  water  under  con- 
siderable pressure. 

As  manufactured  in  America  and  Belgium,  forcite  is  a  thin 
blasting  gelatine,  or  nitro-cotton,  incorporated  with  a  mixture 
of  nitrate  of  soda,  coated  with  molten  sulphur  and  wood  tar. 


20  MODERN    TUNNEL    PRACTICE 

To  counteract  the  stickiness  of  the  tar,  i%  of  wood  pulp  is 
added. 

Atlas  Powder. — This  is  a  composition  of  nitroglycerine,  wood 
fibre,  nitrate  of  soda,  and  2%  to  3%  of  carbonate  of  magnesia. 
It  is  made  in  various  grades,  containing  from  20%  to  75%  of 
nitroglycerine. 

American  Hercules  Powder. — In  the  No.  I  grade  of  this 
powder  the  proportions  and  ingredients  are  stated  to  be  75% 
nitroglycerine,  20%  carbonate  of  magnesia,  2.1%  nitrate  of 
soda,  1.05%  chlorate  of  potash,  i%  white  sugar. 

The  carbonate  of  magnesia  is  here  employed  as  the  absorb- 
ent. The  claim  is  made  that  the  resultant  fumes  from 
explosion  are  not  so  bad  in  their  effect  upon  the  miners  as  those 
arising  from  dynamite.  Mr.  Eissler  says  that  this  advantage 
may  be  due  to  the  presence  of  the  alkaline  absorbent,  which 
gives  off  gases  which  contain  no  carbonic  oxide. 

Judson  Powder. — In  this  powder,  instead  of  absorbing  the 
nitroglycerine,  as  in  the  case  of  dynamite,  a  thin  film  of  $% 
to  15%  of  nitroglycerine  is  used  as  a  final  operation  to  coat 
grains  of  non-absorbent  and  non-hygroscopic  oxidizing  salts. 
This  process  is  carried  out  in  various  ways. 

One  example  of  the  oxidizing  salts  mentioned  by  Eissler  is 
made  up,  by  weight,  of  15  parts  sulphur,  3  parts  resin,  2  parts 
asphalt,  70  parts  nitrate  of  soda,  10  parts  anthracite  coal.  The 
sulphur,  resin  and  asphalt  are  melted  together  and  well  stirred ; 
and  to  this  melted  mixture  are  added  the  nitrate  of  soda  and 
the  coal,  both  pulverized  and  thoroughly  dry.  The  mixture 
is  then  gently  stirred  until  so  cool  that  the  grains  cease  to  ad- 
here together,  and  these  grains  are  thoroughly  varnished.  The 
nitroglycerine  is  added  when  the  explosive  is  to  be  used.  This 
powder  is  extensively  used,  is  cheap,  and  is  more  powerful  than 
common  mining  powder,  depending  for  its  strength  on  the  per- 
centage of  nitroglycerine. 

Joveite — This  substitute  for  dynamite  belongs  to  the  picric- 
acid  class  of  powders.  It  is  made  by  melting  crystals  'of  solid 
nitronaphthaline  and  solid  picric  acid  in  a  steam- jacketed  kettle 
or  mixer,  after  which  solid  nitrate  of  soda  is  added.  The  prod- 


EXPLOSIVES  21 

uct  is  a  yellow,  granular  substance  resembling  sawdust  or 
cornmeal.  This  product  is  sold  either  in  the  granulated  state 
or  is  made  up  into  cartridges,  resembling  outwardly  "sticks" 
of  dynamite. 

Joveite  is  fired  with  a  cap,  either  with  a  fuse  or  with  an  elec- 
tric battery.  If  the  cap,  however,  is  not  thrust  into  the~end 
of  the  stick,  but  placed  about  f  of  an  inch  away  from  It,  the 
joveite  will  not  explode.  In  a  test  held  in  1903  one  capped  stick 
was  placed  within  2  inches  of  the  other  sticks  lying  around  it, 
and  fired.  The  capped  stick  exploded,  but  the  others  did  not. 
As  joveite  contains  no  liquid  in  its  original  composition,  it  is  a 
solid,  and  should  not  freeze  any  more  than  black  powder.  And 
as  it  is  made  at  a  high  temperature,  Charles  E.  Munroe, 
Ph.D.,  of  Columbian  University,  states  that  it  is  not  subject  to 
changes  of  condition  or  alternating  heat  and  cold.  He  says  that 
the  powder  showed  no  change  after  being  exposed  in  open 
boxes  in  a  room  for  four  years.  Its  makers  also  claim  that  the 
fumes  of  burnt  joveite  produce  no  ill  effect  upon  the  work- 
men. It  can  be  used  in  wet  holes  or  under  water,  though  it 
should  not  be  left  there  long  enough  for  the  nitrate  of  soda 
to  leak  out.  This  difficulty  is  overcome  by  its  makers,  by  put- 
ting it  into  cloth-covered  wrappers  entirely  impervious  to  water. 

The  explosive  power  of  joveite,  as  compared  with  nitro- 
.glycerine  powders,  is  not  stated ;  but  as  tested  in  a  steel  mortar, 
is  over  three  times  stronger  in  projectile  force  than  black 
powder.  As  made  in  three  grades,  joveite  No.  i  is  said  to  be 
equivalent  to  20%  dynamite ;  No.  2  is  equivalent  to  40%  dyna- 
mite, and  No.  3XX  is  the  equivalent  of  60%  dynamite.  Bulk 
for  bulk,  joveite  weighs  fully  one-third  less  than  most  dyna- 
mites of  equal  grade.  It  was  patented  in  1894. 

Sprengel  Class  of  Explosives. — In  1873  Dr.  Hermann 
Sprengel  introduced  a  type  of  explosive  which  had  for  its  char- 
acteristic feature  the  admixture  of  an  oxidizing  with  a  com- 
bustible agent,  at  the  time  or  just  before  it  was  to  be  used,  the 
separate  constituents  of  the  mixture  being  non-explosive. 

Dr.  Sprengel  originally  used  substances  one  or  all  of  which 
would  be  liquid,  as  liquids  better  assured  a  speedy  and'  intimate 


22  MODERN    TUNNEL    PRACTICE 

mixture.  But  it  was  found  by  experience  that  there  was  too 
much  danger  attending  the  mixture  of  liquids  by  ordinary 
workmen,  and  other  substances  were  discovered  which  were 
safer- and  still  retained  the  advantages  of  the  Sprengel  prin- 
ciple, so  far  as  transportation  and  mixing  were  concerned. 

Rack-a-Rock. — This  is  the  most  widely  known  of  the  Spren- 
gel mixtures.  Gen.  Abbot  says  that  the  best  results  are  secured 
when  rack-a-rock  is  made  of  79  parts  of  potassium  chlorate 
and  21  parts  of  mono-nitrobenzene.  These  ingredients  may 
be  safely  transported  and  stored  separately.  When  required 
for  use  the  chlorite  cartridges  are  placed  in  a  special  wire  basket 
and  dipped  into  a  vessel  holding  the  liquid  mono-nitrobenzene 
for  three  to  six  seconds,  depending  on  the  size  of  the  cartridges. 
The  cartridges  are  then  allowed  to  drain,  and  in  ten  minutes 
they  are  ready  for  use. 

According  to  Gen.  Abbot,  rack-a-rock  has  a  specific  gravity 
of  1.7,  and  is  a  compact  solid.  It  requires  a  very  powerful  de- 
tonator to  explode  it,  and  it  decrepitates  with  difficulty  when 
hammered  on  an  anvil.  Gen.  John  Newton,  Corps  of  Engi- 
neers, U.  S.  A.,  employed  240,399  pounds  of  this  explosive  in 
blowing  up  Flood  Rock,  in  the  East  River,  New  York. 

Hellhoffite. — This  compound  was  invented  in  1885  by  Hell- 
hoff  and  Gruson.  It  is  made  of  approximately  47  parts  of 
meta-di-nitrobenzene  and  53  parts  of  nitric  acid.  On  mixture  it 
appears  as  a  dark-brown  liquid.  If  mixed,  and  not  immediately 
wanted  for  use,  the  di-nitrobenzene  can  be  recrystallized  by 
gradually  adding  water  to  the  mixture,  the  acid  being  wasted. 

To  develop  the  full  force  of  this  compound  a  detonator  is 
required  that  is  twice  as  powerful  as  that  used  with  dynamite. 
It  is  more  powerful  than  nitroglycerine  in  the  ratio  of  106  to 
100;  and  it  can  be  stored  and  transported  with  perfect  safety. 
But  it  is  a  liquid ;  the  acid  is  volatile  and  can  only  be  stored  in 
perfectly  tight  vessels ;  it  cannot  be  used  for  submarine  work, 
as  water  renders  it  completely  inexplosive;  and  the  acid  acts 
injuriously  on  the  copper  casing  of  the  detonators. 

Other  Sprengel  Compounds. — Other  explosives  of  this  type 
are  known  as  Oxonite,  Plancastite,  Romite,  etc.  But,  while 


EXPLOSIVES  23 

their  great  power  as  explosive  agents  is  undoubted,  their  prac- 
tical value  is  greatly  diminished  by  reason  of  the  relatively  high 
degree  of  intelligence  required  in  their  proper  admixture;  by 
the  fact  that  they  are  liquids;  by  the  serious  objection  made  to 
the  fumes  of  the  exploded  ingredients  in  confined  places,  and 
by  the  fact  that  they  cannot  be  used  under  water.  They  Thay 
have  value  for  military  operations,  as  their  proper  manipula- 
tion would  be  thus  generally  assured. 

Safety  or  Time  Fuses. — The  ordinary  or  Bickford  fuse 
includes  a  core  o£  meal-powder,  tightly  compressed  and  en- 
closed in  a  wrapper  of  spun  yarn  impregnated  with  a  water- 
proof composition.  These  fuses  are  made  in  various  forms, 
with  "single"  and  "double"  tape,  etc.,  the  thicker  wrapping  be- 
ing employed  in  damp  places. 

In  using  any  make  of  safety  fuse  it  is  well  to  carefully  deter- 
mine the  rate  of  burning.  This  is  simply  done  by  attaching 
different  lengths  of  fuse  to  blasting  caps  and  noting  the  time 
necessary  for  the  powder  to  explode  the  cap.  With  the  rate  of 
burning  known,  the  miner  can  cut  a  sufficient  length  of  fuse  to 
allow  him  ample  time  to  retire  to  a  place  of  safety  before  the 
charge  is  exploded. 

In  capping  a  fuse,  examine  the  cap  carefully  to  see 'that  no 
particle  of  the  sawdust  in  which  the  caps  are  packed  remains 
inside.  Cut  the  end  of  the  fuse  cleanly  and  squarely,  and  insert 
it  in  the  cap  until  it  is  in  close  contact  with  the  upper  surface 
of  the  fulminate.  The  fuse  must  fit  the  cap  snugly.  If  the 
fuse  is  too  large,  pare  it  down ;  if  it  is  too  small,  wrap  it  with 
paper  until  it  fits  snugly.  When  this  is  all  done  the  free  end 
of  the  cap  is  tightly  crimped  to  the  fuse,  so  that  it  cannot  be 
detached.  If  the  charge  to  be  fired  is  in  a  very  damp  place, 
or  under  water,  the  joining  of  the  cap  and  the  fuse  should  be 
made  watertight  by  a  coating  of  paraffine,  tar,  shellac,  or  some 
such  substance. 

Primer. — The  primer  is  the  cartridge  to  which  the  cap  and 
fuse  are  attached.  This  primer  is  completed  and  the  cap  at- 
tached to  the  cartridge  as  follows :  One  end  of  the  wrapper  of 
the  cartridge  is  opened — in  the  case  of  a  dynamite  cartridge — 


24  MODERN    TUNNEL    PRACTICE 

and  a  smooth,  round  stick,  slightly  larger  in  diameter  than  the 
cap,  is  used  to  make  a  hole  in  the  center  of  the  cartridge.  In 
this  hole  the  cap  is  inserted ;  the  cartridge  is  compressed  by  the 
hand  so  as  to  come  in  contact  with  the  cap,  and  the  end  of  the 
paper  wrapper  is  then  drawn  around  the  fuse  and  tied  tightly 
with  a  string.  The  cap  should  only  have  two-thirds  of  its 
length  inserted  into  the  cartridge;  otherwise,  the  burning  fuse 
might  set  fire  to  the  cartridge  before  igniting  the  fulminate  in 
the  cap. 

The  completed  primer  is  preferably  placed  in  the  center  of 
the  charge  to  be  fired,  and  always  in  contact  with  the  charge. 
The  object  of  the  blast  in  each  individual  case  must  determine 
the  placing  of  the  charge  itself. 

If  only  one  cartridge  is  used  in  a  hole,  it  is  still  advisable  to 
use  a  primer,  using  for  this  purpose  a  piece  of  cartridge  about 
two  inches  long,  to  which  the  fuse  and  cap  are  attached  as 
described  above. 

Electric  Firing. — The  ordinary  safety  fuse  has  several  serious 
disadvantages  when  employed  to  explode  dynamite  cartridges. 
It  is  liable  to  "miss  fire,"  and  to  "hang  fire,"  the  last  of  these  be- 
ing the  cause  of  innumerable  accidents.  It  is  also  impossible  to 
secure  simultaneous  action  in  the  explosion  of  several  charges, 
and  there  is  a  consequent  loss  of  effect  in  the  explosion. 

In  using  the  electric  system  of  firing  dynamite  cartridges, 
the  electric  cap  is  entirely  buried  in  the  primer-cartridge ;  and, 
instead  of  tying  the  paper  wrapper  around  the  fuse,  the  fuse 
wires  are  doubled  back  and  fastened  to  the  primer  by  two  half- 
hitches. 

Electric  Fuse. — The  so-called  low,  medium  and  high-tension 
electric  fuses  only  differ  essentially  in  the  manner  of  igniting 
them.  The  low-tension  type  acts  by  the  heating  of  a  very  fine 
wire,  imbedded  in  a  proper  priming,  and  the  uniting  of  insu- 
lated conductors.  The  medium  and  high-tension  fuses  are  fired 
by  the  passage  of  the  electric  spark  over  a  break  in  the  me- 
tallic circuit,  this  spark  igniting  a  suitable  priming. 

Each  electric  fuse  has  two  insulated  conductors,  a  plug 
to  receive  and  firmly  hold  the  ends  of  the  conductors  near 


EXPLOSIVES  25 

to,  but  not  touching  each  other ;  a  small,  sensitive  priming  prop- 
erly arranged  at  the  plug  for  firing,  and  a  metallic  cup  or  cap, 
usually  containing  fulminating  mercury,  representing  the  de- 
tonating charge.  The  so-called  fuse-wires,  extending  out  from 
the  cap,  must  always  be  well  insulated,  and  should  not  be  less 
than  two  feet  long. 

Connecting  or  Lead  Wires — These  two  wires  conduct  the 
electric  current  from  the  igniting  apparatus  to  the  primer-car- 
tridge. One  of  these  wires  conducts  the  electricity  to  the  cap, 
and  is  known  as  the  "conducting  wire" ;  the  other  completes 
the  circuit  back  to  the  igniter,  and  is  known  as  the  "return 
wire." 

These  wires  should  both  be  well  insulated,  for  should  bare 
wires  touch  each  other  or  the  ground  a  "short  circuit"  may  be 
formed  and  the  firing  of  the  charge  prevented.  Bare  wires  can 
be  used  in  special  cases  by  placing  them  on  poles  and  insulators. 
The  best  connecting  wires  are  made  of  perfectly  clean  copper 
wire  covered  with  india  rubber  insulation.  For  short  distances 
wires  may  be  insulated  with  paraffined  cotton  yarn,  and  these 
answer  fairly  well. 

Firing  Apparatus. — Various  forms  of  igniting  apparatus  are 
employed  in  connection  with  the  use  of  electric  fuses.  But  the 
favorite  machine — and  one  that  is  compact,  strong  and  reliable 
— is  the  magneto-electric  apparatus.  This  machine,  as  usually 
supplied,  is  contained  in  a  wooden  box  about  16x8x5  inches, 
and  weighs  about  eighteen  pounds.  Outwardly,  this  box  shows 
a  strap-handle,  two  brass  binding-posts  for  the  lead  wires,  and 
a  central  firing-bar  working  vertically.  Without  entering  into 
the  detail  of  the  inner  mechanism,  it  is  sufficient  to  say  that 
the  novelty  of  this  device  lies  in  the  method  adopted  for  ro- 
tating a  Siemens  armature  between  the  soft  iron  prolongations 
of  the  cores  of  an  electro-magnet. 

The  brass  firing-bar  has  a  wooden  handle  at  the  top,  and  one 
side  of  the  bar  has  rack  teeth  cut  upon  it,  engaging  in  a  loose 
pinion  fitting  over  the  armature  spindle  prolonged.  When  the 
bar  is  descending  a  clutch  holds  the  spindle  to  the  pinion,  the 
pinion  rotates,  and  a  strong  electrical  current  is  produced;  as 


26  MODERN    TUNNEL    PRACTICE 

the  bar  ascends  the  clutch  releases  the  spindle ;  there  is  no  ro- 
tation, and  action  is  thus  restricted  to  the  one  downward  move- 
ment of  the  bar.  The  purpose  of  this  one-direction  action  is 
to  avoid  possible  accidents  in  manipulating  the  machine. 

To  use  this  igniter,  the  ends  of  the  two  connecting  wires  are 
well  cleaned,  inserted  in  the  two  binding-posts  on  the  box,  and 
firmly  held  in  position  by  the  binding  screws.  The  firing-bar 
is  then  pulled  up  to  its  full  length,  and  when  all  is  ready  the 
bar  is  pushed  down  with  a  quick,  uniform  motion.  Electricity 
is  thus  generated,  transmitted  by  the  wires  to  the  cap,  and  the 
charge  is  exploded. 

This  machine  may  be  temporarily  disabled  by  two  causes: 
( i )  Dust  or  dirt  may  get  between  the  platinum  contact-points 
inside  the  box.  To  remedy  this,  remove  the  rear  of  the  case 
and  use  a  piece  of  fine  emery-cloth  on  the  contact-points.  (2) 
The  surface  of  the  transformer  or  commutator  may  become 
tarnished.  In  this  case  open  the  rear  of  the  box  as  before,  and 
withdraw  the  firing-bar  by  first  taking  out  a  small  pin  at  the 
bottom  of  the  bar.  The  shelf  holding  the  internal  mechanism 
can  now  be  partially  withdrawn ;  the  springs  pressing  upon  the 
commutator  and  the  spindle-yoke  can  be  disconnected,  and  the 
face  of  the  commutator  can  then  be  cleaned  with  emery-cloth. 

Precautions  to  be  Observed  in  Firing  -High  Explosives. — In 
his  lectures  on  explosives,  delivered  before  the  U.  S.  Artillery 
School,  Lieut.  W.  Walke,  U.  S.  A.,  gives  some  general  advice 
upon  the  use  of  electricity  in  firing  high  explosives.  This  ma- 
terial is  here  condensed,  with  some  additional  matter  added. 

To  reap  the  full  benefit  of  this  method  especial  attention  must 
be  paid  to  the  preparation  of  the  connecting  wires.  To  pre- 
vent the  ends  of  the  leading  wires  from  being  constantly  blown 
off,  the  "fuse  wires"  and  the  "connecting  wires"  should  be  con- 
nected by  a  coupling  of  two  short  wires.  And,  if  practicable, 
the  fuse  wires  should  be  long  enough  to  extend  at  least  six  or 
eight  inches  outside  of  the  bore-hole. 

To  connect  the  fuse  and  leading  wires,  pare  off  two  to  three 
inches  of  the  insulating  material  from  the  ends  of  the  wires 
and  clean  these  ends  with  sand-paper.  To  join  the  wires,  bend 


EXPLOSIVES  27 

back  the  ends  of  the  wires  to  form  hooks;  hook  the  wires  to- 
gether, and  then  twist  the  ends  of  the  wires  closely  and  firmly 
around  the  hooks.  Some  old  miners  recommend  as  a  better 
method  the  crossing  of  the  ends  of  the  wire,  and  then  making 
about  six  close  twists  about  the  standing  parts  of  the  wires. 
In  either  case  a  close,  tight  twist  is  necessary,  as  a  slack  joint 
makes  a  bad  connection. 

In  very  damp  ground  this  joint  may  be  protected  by  slip- 
ping a  small  piece  of  thin  rubber  tubing  over  one  wire  before 
joining,  and  when  the  connection  is  made  the  tubing  can  be 
slipped  over  it  and  tightly  tied  at  the  ends. 

A  rule  of  great  importance  is :  Never  connect  the  fuse  and 
the  connecting  wires  until  you  are  absolutely  sure  that  one,  at 
least,  of  the  leading  wires  is  disconnected  from  the  igniting 
apparatus.  The  very  last  thing  to  be  done  before  actually  firing 
the  charge  is  the  connecting  of  the  leading  wires  with  the  firing 
apparatus.  All  other  connections  must  be  made  before  this  is 
done,  and  every  precaution  taken  to  see  that  the  charge  is  ready 
for  explosion. 

All  bare  joints  in  connecting  wires  should  be  kept  off  the 
ground  and  out  of  the  water;  if  this  cannot  be  done,  protect 
the  joints  as  described  above. 

Special  reels  are  made  for  handling  the  leading  wires,  and 
their  use  will  be  found  to  be  economical. 

By  proper  attention  to  all  these  details,  Lieut.  Walke  says 
that  it  is  possible  to  simultaneously  fire  fifteen  charges  in  the 
same  circuit. 

Handling  and  Storing  of  Explosives — In  his  "Handbook  on 
Modern  Explosives"  Mr.  M.  Eissler  gives  some  excellent  ad- 
vice in  this  direction,  summarized  as  follows : 

1.  Put  dynamite  into  close  quarters,  and  hold  it  there  by 
the  most  unyielding  method  of  confinement  at  command.     Let 
there  be  no  vacancies  about  the  charge  of  any  kind  or  degree. 

2.  Always  tamp  if  you  can.     But  use  a  wooden  rammer; 
never  use  an  iron  or  steel  bar  with  any  explosive. 

3.  If  you  value  your  fingers,  do  not  fool  with  the  cap  "to 
see  what  is  in  it."  * 


28  MODERN    TUNNEL    PRACTICE 

4.  The  charge  must  fit  and  fill  the  bottom  of  the  bore-hole, 
and  be  packed  solid. 

5.  Never  pick  out  a  "miss  fire"  of  powder  or  dynamite,  but 
gently  clear  out  the  hole  to  within  about  eight  inches  of  the 
old  charge.    Then  place  a  fresh  cartridge,  or  a  piece  of  one,  in 
the  hole,  and  fill  it  up  again  as  before.     Fire  this,  and  it  will 
explode  the  original  charge  below. 

6.  Never  attempt  to  roast,  toast  or  bake  frozen  dynamite, 
and  never  put  it  into  heated  vessels  or  on  boilers.     The  only 
absolutely  safe  method  of  thawing  out  frozen  dynamite  is  to 
keep  it  in  a  room  at  summer  heat  and  away  from  the  fire  until 
it  is  soft. 

7.  Never  put  a  cap  into  a  charge  or  a  primer  until  you  are 
ready  to  use  it.     And  after  the  charge  or  primer  is  capped 
never  let  it  leave  your  hands  until  it  is  put  into  the  hole.    Keep 
all  caps  away  from  the  dynamite  until  the  charge  is  to  be  fired. 
Invariably  prepare  your  primer  away  from  the  explosive. 

8.  Never  allow  smoking,  or  other  forms  of  fire,  near  the  ex- 
plosive.    Powder  and  other  explosives  burn  rapidly,  especially 
when  loose;  and  if  any  caps  are  incautiously  left  near  by  they 
may  be  fired  and  a  dangerous  explosion  result. 

9.  Do  not  get  nitroglycerine  upon  your  fingers.     It  will  be 
absorbed  by  the  skin  and  cause  headache,  or  worse. 

10.  For  powder,  use  the  best  quality  of  double-tape  fuse; 
it  is  always  the  cheapest  and  best  in  securing  results.     When 
you  know  that  the  ground  is  almost  dry  you  can  use  single- 
tape  fuse. 

Frozen  Dynamite — When  dynamite  and  other  nitroglycerine 
compounds  are  frozen  they  can  only  be  exploded  by  very  strong 
primers;  but  the  effect  of  the  explosion  is  more  violent  than 
when  exploded  in  a  soft  state. 

As  a  rule,  the  frozen  mass  does  not  become  uniformly  hard 
throughout,  because  of  slight  variations  in  the  proportions  of 
nitroglycerine  in  different  parts  of  the  mixture,  and  partly  be- 
cause the  external  portion  of  the  cartridge  will  be  more  thor- 
oughly frozen  than  the  interior,  unless  the  exposure  to  cold  is 
very  prolonged.  It  may  happen  that  partly  frozen  or  wholly 


EXPLOSIVES 


29 


unfrozen  dynamite  may  be  more  or  less  completely  enclosed  in 
a  strong  crust  of  perfectly  frozen,  and  comparatively  very  cold 
dynamite.  On  exposure  to  considerable  heat,  rapidly  applied, 
some  part  of  the  cartridge  may  be  ignited  and  the  unfrozen 
portion  exploded.  In  such  a  case  the  hard,  frozen  dynamite 
practically  acts  as  the  metal  envelope  of  a  detonator ;  the  ex- 
plosive is  confined  and  in  a  condition  to  exert  extreme  violence. 
The  explosion  of  the  unfrozen  dynamite  acts  as  a  detonator  or 
primer,  and  explodes  the  remainder  of  the  dynamite. 

For  the  reasons  given  above,  Sir  F.  A.  Abel  points  out  the 
danger  of  assuming  that  because  frozen  dynamite  is  less  sen- 
sitive to  the  effect  of  a  blow,  or  to  initiative  detonation,  than 
is  the  thawed  material,  it  may  be  submitted  to  the  action  of 
heat,  for  the  purpose  of  thawing  it,  without  using  special  care. 

Thawing  Frozen  Dynamite — There  are  only  two  ways  of 
safely  thawing  out  frozen  dynamite :  ( i )  By  placing  the  frozen 


FIG.  4. — Dynamite  Thawer:  Hamilton  Powder  Co. 

cartridges  in  a  room  heated  to  a  summer  heat  by  steam  pipes, 
being  careful  to  keep  the  explosive  away  from  the  pipes  them- 
selves. (2)  By  placing  the  cartridges  in  a  suitably  constructed 
vessel  surrounded  by  water  heated  to  125°  Fahr.  The  water 
should  be  heated  separately  and  poured  into  the  thawer.  Sheet 
zinc  is  the  best  material  for  this  thawer,  though  galvanized 
iron  is  largely  used. 

A  form  of  thawer  is  sold  which  is  built  somewhat  upon  the 
model  of  a  glue-pot.    It  has  a  hot-water  receptacle,  into  which 


30  MODERN    TUNNEL    PRACTICE 

fits  another  annular  vessel  for  holding  the  cartridges.  The 
water  space  between  the  inner  vessel  and  the  outer  wall  should 
be  at  least  two  inches  wide.  For  thawing  large  quantities  of 
dynamite  at  a  time,  the  following  plan  is  shown  in  Mr.  De 
Kalb's  "Manual,"  as  recommended  by  the  Hamilton  Powder 
Company : 

A  barrel  has  fitted  into  it  a  circulating  hot-water  system  of 
pipes,  with  an  expansion  pipe.  This  pipe  system  passes  through 
a  wall,  and  is  heated  by  a  stove.  The  barrel  is  filled  with  water, 
which  is  heated  by  the  hot  water  circulating  in  the  pipes,  and 
kept  hot.  The  frozen  dynamite  is  put  into  the  zinc  or  gal- 
vanized iron  receptacle  suspended  in  the  barrel. 

In  using  any  kind  of  thawer,  the  only  way  of  being  sure  that 
there  are  no  accumulations  of  nitroglycerine  in  the  thawer  is 
to  wash  the  thawer  out  after  each  thawing  with  a  strong  solu- 
tion of  washing  soda,  best  applied  warm.  To  the  same  end, 
all  sawdust  should  be  removed  from  the  cartridges  before  they 
are  put  into  the  thawer. 

As  long  as  the  dynamite  feels  lumpy  in  the  cartridges  it  is 
not  properly  thawed.  It  should  be  uniformly  pliable  through- 
out. Aside  from  the  danger  in  loading,  partially  thawed  dyna- 
mite is  less  powerful  in  exploding,  and  it  gives  off  particularly 
noxious  fumes. 

Dynamite-thawing  House — The  dynamite-thawing  house 
shown  in  Fig.  5  is  one  recommended  by  the  commissioners  ap- 
pointed to  investigate  the  explosion  of  dynamite  on  the  Fourth 
Avenue  section  of  the  New  York  Rapid  Transit  Railway,  on 
January  27,  1902.  It  is  intended  to  hold  500  pounds  of  dyna- 
mite. The  special  feature  of  the  design  is  the  arrangement  of 
the  drawers  immediately  back  of  folding  doors,  leaving  no 
space  for  a  man  to  stand  inside  the  magazine;  and  making  it 
unnecessary  to  use  any  form  of  artificial  light  in  handling  the 
dynamite.  An  experimental  house  built  on  this  plan  cost  $200. 

Magazine. — In  the  storage  of  ordinary  black  powder,  im- 
munity from  fire  is  a  first  consideration.  As  it  is  assumed  in 
this  work  that  the  powder  magazine  is  a  more  or  less  temporary 
structure,  the  more  permanent  forms  of  magazines  are  not  here 


EXPLOSIVES 


3T 


discussed  or  described;  and  in  general  the  form  recommended 
is  suitable  for  storing  gunpowder  or  dynamite. 

The  Austrian  law  on.  the  storage  of  all  explosives  requires 
that  the  structure  used  for  this  purpose  should  be  as  light  as 


Sheet  Iron  or 

Tin  covering  throughout 


K— -4'7- - -> 

Vertical       Section. 


Hot .  Water  Pipe  leaves 
Top  of  Heatfr 


Lnc, 

'     NE.WS. 


FIG.  5. — Dynamite-Thawing  House. 

possible.  The  purpose  of  this  law  is  that,  in  case  of  explosion, 
the  building  may  be  completely  disintegrated  and  no  pieces  of 
any  size  be  thrown  to  a  distance,  thus  reducing  the  radius  of 
the  danger  zone  to  a  minimum.  In  England  the  law  demands 


32  MODERN    TUNNEL    PRACTICE 

a  more  substantial  structure,  as  a  precaution  against  fire  and 
burglars.  But  in  a  comparatively  open  country  the  light  struc- 
ture is  preferable.  Storage  in  a  tunnel,  cave,  or  other  similar 
place  should  never  be  permitted,  as  such  places  are  almost  in- 
variably damp,  and  any  powder  containing  nitrates  will  be 
damaged. 

A  suitable  structure  for  the  storage  of  explosives  on  ordi- 
nary contract  work  may  be  described  as  follows :  Use  a  2  x  4- 
inch  frame,  and  cover  with  weather  boarding.  Put  in  a  tongue- 
and-grooved  tight  floor,  blind-nailed,  and  the  inside  walls  and 
ceiling  may  be  sheathed  with  the  same  stuff.  The  roof  should 
be  A-form,  and  a  covering  of  strong  tar  paper  will  make  it 
tight.  When  there  is  danger  from  fire  the  roof  and  the  outside 
walls  may  be  covered  with  the  lightest  kind  of  steel  shingles. 
A  structure  of  this  kind,  6x6  feet  on  the  base,  and  6  feet  high, 
will  hold  about  216  kegs  of  powder. 

As  a  further  precaution,  bottom  ventilators  should  be  put  in, 
with  the  openings  covered  with  wire  to  keep  out  vermin ;  and 
a  hooded  ventilator  pipe  should  be  extended  from  the  ceiling 
through  the  roof.  In  a  region  where  there  is  danger  from  rifle 
balls,  the  magazine  may  be  built  with  a  6-inch  space,  enclosing 
fine,  dry  sand,  extending  upward  as  high  as  the  kegs  or  cases 
of  explosives  are  to  be  piled.  Prof.  Courtenay  De  Kalb,  in  a 
"Manual  of  Explosives,"  issued  by  the  Ontario  Bureau  of 
Mines,  says  that,  by  actual  experiment,  the  ball  from  a  Lee- 
Metford  rifle,  at  a  range  of  twenty-four  feet,  only  penetrated 
five  inches  into  a  sand  protection  of  this  type. 

Storing — In  magazines,  kegs  of  powder  should  be  kept 
slightly  inclined  on  suitable  racks.  Dynamite,  when  stored  in 
tiers  of  cases,  should  have  wooden  battens  between  the  tiers 
to  insure  ventilation  and  to  lessen  danger  from  friction. 

No  fulminates,  or  caps,  and  no  loose  coils  of  fuse  should  be 
stored  in  the  same  building  with  powder  or  dynamite. 

The  building  should  be  kept  very  clean,  and  no  fires  or 
smoking  permitted  in  or  near  it. 

Gunpowder  kegs  should  be  rolled  over  every  two  or  three 
days,  to  prevent  caking.  Cases  of  dynamite  should  be  turned 


EXPLOSIVES  33 

over  every  two  weeks.    This  tends  to  keep  the  dynamite  homo- 
geneous in  composition  and  is  economical. 

No  keg  of  powder  or  case  of  dynamite  should  be  opened 
inside  the  magazine.  This  should  be  done  in  a  distant  and 
special  small  building,  never  containing  at  one  time  more  than 
200  pounds  of  an  explosive.  Keep  kegs  closed  after  taking  out 
what  powder  is  wanted.  In  the  case  of  dynamite^  unpack  the 
cartridges  and  wipe  off  the  sawdust,  which  usually  contains 
some  nitroglycerine.  Carefully  remove  this  sawdust  and  the 
boxes  and  burn  them  at  some  convenient  distant  point  Lay 
the  cartridges  on  their  sides  on  planed  boards,  and  keep  these 
boards  clean  at  all  times  by  removing  oily  stains  with  washing 
soda. 


CHAPTER    III 

BLASTING 

General  principles  to  be  observed  in  proportioning  the  depth  and  diameter 
of  the  holes  to  the  work  to  be  done — The  line  of  least  resistance — The 
location  of  bore-holes — The  square  and  the  V-shaped  cut — The  con- 
sumption of  explosives — Method  followed  on  the  New  York  Subway — 
Testing  the  blasting  properties  of  rock — Loading  with  black  powder — 
Effect  of  nitro-glycerine  fumes,  and  precautions  to  be  observed — Hints 
on  power-drilling — To  prevent  the  crushing  of  shaft-timbers  by  flying 
rock. 

No  rigid  rules  can.  be  laid  down  for  the  diameter  and  depth 
of  holes,  the  direction  these  holes  should  take,  the  distance 
apart  of  holes,  or  the  amount  of  the  charge  placed  in  each  hole. 
The  character  of  the  material,  the  purpose  of  the  blast,  and  a 
number  of  other  and  varying  conditions  will  here  control.  Effi- 
cient work  in  blasting  is  a  matter  of  experience  and  good  judg- 
ment on  the  part  of  the  miner,  and  this  cannot  be  gained  from 
books.  But  writers  on  this  subject  lay  down  some  general  and 
fundamental  rules  which  must  be  observed  in  the  interest  of 
systematic,  economical  work. 

Prof.  De  Kalb,  in  his  "Manual,"  quoting  from  the  works  of 
Daw,  Oscar  Guttmann  and  others,  lays  down  the  following 
points  of  prime  importance  and  general  application : 

1.  The  strength  and  quantity  of  the  explosive  should  be  prop- 
erly proportioned  to  the  cohesive  strength  or  resistance  of  the 
rock. 

2.  The  "burden,"  or  line  of  least  resistance  (i.  e.,  the  shortest 
line  that  can  be  drawn  from  the  charge  in  the  bore-hole  to  the 
outer  free  face  of  the  rock),  should  bear  a  proper  relation  to 
the  strength  of  the  explosive  and  the  resistance  of  the  rock. 

3.  If  the  working  face  of  the  rock  is  so  blasted  as  to  leave 
two  or  more  free  faces,  instead  of  one,  for  further  blasts,  the 

34 


BLASTING  35 

power  required  to  overcome  the  resistance  of  the  rock  will  be 
reduced,  and  explosives  can  be  economized. 

4.  A  seam  or  fissure  is  a  valuable  aid  in  blasting  if  the  hole 
is  so  located  as  to  take  advantage  of  this  weakness ;  on  the  other 
hand  the  power  of  the  explosive  may  be  expended  along  such  a 
seam  without  doing  useful  work,    if    the    hole  is  improperly 
located. 

5.  Breaking  to  regular  benches  and  faces  is  more  economical 
than  irregular  breaking,  because  the  condition  of  the  rock  can 
be  more  carefully  observed,  the  subsequent  bore-holes  can  be 
more  intelligently  placed,  and  it  facilitates  the  setting  up  and 
handling  of  machine  drills.     It  is  also  more  convenient  for 
hand-drilling. 

6.  Simultaneous  firing  of  charges  is  more  economical,  in 
general,  than  single  or  series  shots;  for  the  adjacent  charges 
assist  each  other,  reducing  the  amount  of  explosive  required 
and  the  total  length  of  holes  drilled  for  removing  any  given 
volume  of  rock. 

7.  Careful  charging  greatly  increases  the  efficiency  of  the 
explosion. 

8.  In  the  case  of  high  explosives  a  well  prepared  primer  is 
the  key  to  a  successful  detonation  of  the  charge.    Other  things 
being  equal,  all  efficiency  depends  on  this. 

9.  The  efficiency  of  all  explosives,  including  high  explosives, 
depends  to  a  considerable  extent  upon  the  kind,  length  and  de- 
gree of  compactness  of  the  tamping. 

10.  The  object  of  blasting  in  a  tunnel,  quarry  or  mine  is  to 
rupture  the  rock  so  that  it  may  be  removed ;  hence  only  enough 
explosive  should  be  used  to  do  this.      When    fragments    are 
thrown  more  than  a  few  feet  by  a  blast,  it  is  generally  an  evi- 
dence that  too  large  a  charge  was  used  for  the  length  of  the 
line  of  least  resistance. 

In  the  accompanying  illustration,  Fig.  6,  B  N  is  the  bore- 
hole, W  L  is  the  shortest  line  measured  from  the  center  of  the 
charge  to  the  free  face  A  K.  M  0  is  the  charge,  which  should 
be  about  twelve  times  as  long  as  the  diameter  of  the  bore  at  the 
bottom ;  R  S  K  is  the  outline  of  the  new  face  after  blasting. 


36  MODERN    TUNNEL    PRACTICE 

To  obtain  the  best  results  the  line  of  least  resistance  W  L 
should  be  perpendicular  to  the  bore-hole  and  shorter  than  the 
bore-hole.  If  it  is  not  shorter  the  force  of  the  explosion  will 
exert  itself  in  the  direction  of  the  bore-hole,  and  the  result  will 
be  a  crater,  or  a  so-called  "gun,"  with  relatively  little  effect. 

In  very  strong,  compact  rock  the  distance  between  holes,  in 
simultaneous  firing,  should  be  at  least  twice  the  length  of  the 
line  of  least  resistance;  for  average  strong  rock,  ij  to  2  times; 


FIG.  6. — Blasting  Nomenclature. 

for  moderately  strong  rock,  i  to  i^  times,  and  for  weak  rock 
this  distance  should  not  exceed  the  length  of  the  line  of  least 
resistance. 

The  lines  of  least  resistance  should  be  proportional  in  length 
to  the  diameter  of  the  bore-holes,  and  Mr.  Eissler  gives  the 
following  table  on  this  head  : 


No.  i. 

"      2. 

"     3- 


DIAMETER  OF  BORE  HOLES. 

1^4  in.  iK  in. 

LINES  OF  LEAST  RESISTANCE. 

3Y2  feet.  4  feet. 

33A     "  5     " 

5       "  6    " 


5  feet. 

7    " 


Mr.  Eissler  gives  the  corresponding  depth  of  the  bore-holes 
as:  No.  i,  equal  to  line  of  least  resistance;  No.  2,  i|  times 
that  length ;  No.  3,  twice  that  length. 


BLASTING 


37 


The  economy  in  simultaneous  firing  varies  with  the  strength 
of  the  rock ;  but  it  may  be  stated  as  an  average,  that  there  is  a 
saving  of  about  25%  in  the  explosives  used.  Under  the  best 
conditions  there  is  also  an  economy  of  about  24%  in  the  boring, 
depending  on  the  distance  apart  of  bore-holes. 

Locating  Bore-holes — In  tunnel  driving  or  shaft-sinking,  the 
first  holes  are  drilled  for  the  purpose  of  "unkeying"  the  face. 
If  there  is  a  persistent  joint  or  seam,  advantage  should  be 
taken  of  this  seam,  and  the  "key"  may  be  thus  broken  out  to 
the  full  depth  of  the  cut  with  a  minimum  of  explosive.  In 
homogeneous  rock  a  square  of  V-shaped  center  cut  is  generally 
adopted. 

Square  Center  Cut — Again  quoting  fromDeKalb's  "Manual," 
we  have  the  plan  and  elevation  of  a  square  center  cut  (Fig.  7) 


FIG.  7.  —  The  Square  Center-cut. 


in  a  rock  heading  7  feet  high  and  6  feet  wide.  The  small  cir- 
cles in  the  plan  indicate  the  commencement  of  the  holes,  and  the 
parallel  lines  show  their  projection,  or  direction.  The  sectional 
elevation  on  the  line  A  B  shows  this  further,  though  hole  No. 
1  8  is  only  approximately  accurate. 

In  this  heading  20  holes  have  been  bored  reaching  to  a  dis- 
tance of  3  feet  3  inches  from  the  face,  which  is  the  depth  of  the 
cut.  Nos.  i,  2,  3,  and  4  are  the  "unkeying"  shots,  converging 


38  MODERN    TUNNEL    PRACTICE 

to  a  point ;  these  holes  preferably  unite  at  the  point,  and  they 
must  be  fired  simultaneously.  The  remaining  16  holes  are  for 
the  "enlarging"  shots,  to  be  fired  in  two  or  three  successive 
volleys.  The  plan  most  economical  of  powder  would  be  to  fire 
5,  7,  9,  ii  in  a  second  volley;  6,  8,  10,  12  in  the  third;  13,  14, 
15,  16,  17,  1 8,  19,  20  in  the  fourth  and  last  volley.  Conditions, 
however,  might  make  it  more  economical  to  use  larger  charges 
in  6,  8,  10,  12  and  include  them  in  the  same  volley  with  5,  7,  9, 
ii.  The  last  is  one  of  the  trimming-up  shots;  and  to  avoid 
irregularities  in  the  rock  it  is  essential  to  start  the  holes  as  close 
to  the  walls  as  possible,  and  to  give  them  very  little  inclination. 
V-shaped  Center  Cut — In  this  form  of  cut  (Fig.  8)  there  are 
fewer  dry  holes  to  be  bored,  and  the  "key"  can  be  broken  out 


fo'M, 

End  Elevation. 


Cross  Section* 


FIG.  8.— The  V-Shaped  Center-cut. 

with  smaller  charges,  as  I,  2,  3,  4  are  short  holes,  with  corre- 
spondingly short  lines  of  resistance. 

There  are  22  holes  in  this  heading.  Nos.  i,  2,  3,  4  constitute 
the  first  volley,  and  provide  shorter  lines  of  resistance  for  the 
next  shots — 5,  6,  7,  8;  holes  9,  10,  n,  12,  13,  14  make  the  third 
volley ;  and  the  trimming  volley  includes  15,  16,  17,  18,  19,  20, 

21,  22. 

In  the  case  of  both  types  of  cut  here  described,  the  methods 
of  procedure  are  given  as  suggestions  for  economical  work 
under  normal  conditions.  They  must  be  suitably  modified  as 
these  conditions  vary. 

An  example  of  drilling  and  blasting  methods  is  here  taken 


BLASTING  39 

from  the  work  performed  on  the  New  York  Rapid  Transit  tun- 
nel. The  diagrams  (Fig.  9)  further  illustrate  the  remarks 
already  made  on  pointing  and  firing  holes,  and  also  note  the 
usual  nomenclature  for  the  various  holes. 

The  method  of  excavating  the  tunnel  is  substantially  the  sin- 
gle top-heading  and  bench  method  commonly  employed  in  The 
United  States.  Both  heading  and  bench,  however,  were  un- 
keyed,  or  broken  out  by  an  opening  and  a  trimming  cut.  Alto- 
gether 40  holes  were  drilled  and  blasted  in  opening  up  the  full 
tunnel  secticrn.  The  approximate  location  and  depth  of  these 
holes  is  shown  in  the  diagrams,  and  with  the  work  well  under 
way,  the  sequence  of  firing  is  given  in  the  table  below : 


BENCH    HOLES. 


Order  of 
firing. 
I. 
II. 

Kind  of  holes, 
No. 
7  grading. 
5  bench. 

•     Depth, 
feet. 
3  to  5 
9-5 

Charge, 
pounds. 
50 
45 

Climax, 
Dynamite, 
per  cent. 
40 
40 

HEADING  HOLES. 

II.  6  trimming.  3  to  9  42  40 

III.  8  center  cut.  9  56  60 

IV.  8  side.  8  48  40 
V.  6  dry.  8  36  40 

NOTE — All  holes  taper  from  3  to  2%  in.  diameter. 

Consumption  of  Explosives. — The  amount  of  explosive  re- 
quired can  only  be  determined  by  intelligent  experiment  under 
actual  conditions  present.  But  as  a  general  guide  one  authority 
approximately  estimates  this  consumption  as  follows : 

For  small  blasts  in  open  workings,  J  to  \  Ib.  of  black  powder, 
and  i- 1 6  to  -J  Ib.  of  dynamite,  per  ton  of  rock. 

For  large  blasts,  in  open  workings,  \  to  \  Ib.  of  black  powder, 
and  \  to  -J  Ib.  of  dynamite,  per  ton  of  rock. 

For  headings,  tunnels  and  shafts,  ^  to  2  Ibs.  of  dynamite  per 
ton  of  rock. 

In  his  "Handbook  of  Modern  Explosives/'  Mr.  Eissler  gives 
a  table  of  the  quantity  of  explosives  actually  used  in  the  course 
of  tunneling  work  executed  for  the  Glasgow  Corporation  Water 
Works.  The  average  quantity  of  explosives,  etc.,  used  is  given 
for  each  cubic  yard  in  the  several  tunnels. 


40 


MODERN    TUNNEL    PRACTICE 


ER  CUBIC  YARD  OF  EXCAVATION;  REDUCED 

.  LINEAL  YARDS  OF  TUNNEL. 

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BLASTING 


Testing  the  Blasting  Qualities  of  Rock — Professor  De  Kalb,  in 
his  "Manual  of  Explosives,"  gives  the  following  general  direc- 
tions for  testing  a  rock  that  is  to  be  broken ;  or,  in  other  words, 
determining  the  most  efficient  and  economical  charge  for  the 
work  to  be  performed.  Select  a  homogeneous  rock  bench  about 
2  feet  wide  on  top  and  3  feet  high.  In  this  drill  four  or  five 


Cross     Section. 


r»s> 

Longitudinal  Section. 

B.H.  "Bench    Holes       6.  H.  »  Grading  Hole* 
C.H.  -  Cut         »  5.H.  -  Sic/9  n 

Q.H. "  Dry        n  T,H.»  Trimming  » 


FIG.  9. — Drilling  and  Blasting  Methods  on  the  New  York  Rapid  Transit 

Tunnel. 

holes  of  the  standard  diameter,  3  feet  deep,  thus  giving  a  line 
of  least  resistance  equal  in  each  case  to  2  feet.  The  distance  be- 
tween these  holes  should  be  at  least  three  times  the  length  of 
the  line  of  least  resistance,  so  that  one  shot  shall  not  influence 
another  by  opening  up  seams.  Now  charge*  the  several  holes 
with  different  weights  of  the  explosive,  beginning  with  a  quan- 
tity so  small  as  not  to  effect  rupture,  and  increasing  by  regular 
amounts  to  a  charge  that  will  be  more  than  sufficient.  Select 
the  blast  which  has  produced  the  desired  effect  as  the  one  deter- 
mining the  coefficient. 


42  MODERN    TUNNEL    PRACTICE 

For  example:  If  this  hole  were  charged  with  f  Ib.  (0.625 
Ib.)  of  dynamite,  then  the  rock  coefficient  is 

0.625 

=  0.0781 

23(=8) 

The  charge  for  future  blasts  is  then  found  by  multiplying 
the  cube  of  the  length  in  feet  of  the  line  of  least  resistance  by 
this  coefficient.  Thus :  If  this  line  is  2f  feet,  the  amount  of 
dynamite  necessary  would  be  2.753  (=20.797  X  0.0781  = 
1.624  Ib.  As  the  specific  gravity  of  well  compacted,  high- 
grade  dynamite  is  about  1.6,  and  as  the  bore-hole  has  a  diameter 
of  1 1  inches,  the  charge  will  occupy  a  length  of  1.25  feet  in  the 
hole.  This  is  approximately  correct  also  as  to  the  length  of 
charge  in  the  bore-hole,  which  should  have  been  1.5  X  12  =  18 
inches.  Guttmann  recommends  that  where  there  are  more  than 
two  free  faces  the  proper  charge  will  be  as  follows : 

For  3  free  sides,  f  of  the  calculated  charge. 

For  4  free  sides,  -J  of  the  calculated  charge. 

For  5  free  sides,  2-5  of  the  calculated  charge. 

For  6  free  sides,  \  of  the  calculated  charge. 

Loading  with  Black  Powder — The  ordinary  practice  in  load- 
ing a  hole  with  black  powder  may  be  outlined  as  follows :  Re- 
move the  sludge  and  dry  out  the  hole  by  any  proper  material 
tied  to  the  end  of  a  long  rod.  Pour  in  the  powder  so  that  it  does 
not  touch  the  sides  of  the  hole  above  the  charge ;  for  horizontal 
or  inclined  holes,  the  powder  may  be  deposited  in  small  paper 
bags,  closely  pressed  home  by  a  wooden  rod.  Special  water- 
proof cartridges  are  supplied  for  wet  holes.  The  fuse  is  now 
put  in  place,  or  tied  to  the  last  bag  of  powder,  if  bags  are  used. 

Dry  clay  is  next  pressed  over  the  charge,  followed  by  3 
inches  of  ordinary  wet  clay  pressed  in  firmly.  After  this 
further  tamping  may  be  rammed  by  tapping  the  end  of  the 
tamping  stick  with  a  hammer.  Practice  shows  that  the  amount 
of  tamping  desirable  is  determined  by  the  diameter  of  the  hole 
and  not  by  the  volume  of  the  charge.  The  least  depths  of  tamp- 
ing material  admissible  are :  For  a  hole  2  inches  in  diameter,. 


BLASTING  43 

7  inches  of  tamping;  for  a  2^-inch  hole,  18  inches ;  for  a  3-inch 
hole,  20  inches.  The  depth  of  tamping  should  always  be  some- 
what in  excess  of  these  figures. 

When  Dynamite  Is  Used. — Mr.  Eissler  gives  some  useful  gen- 
eral directions  relating  to  the  drilling  and  loading  of  holes  with 
dynamite,  condensed  as  follows  : 

As  a  general  rule  the  drill  holes  and  charges  for  dynamite 
can  be  and  should  be  comparatively  small.  In  heavy  workr 
however,  the  holes  should  be  larger  in  size  and  less  in  number, 
and  the  amount  of  dynamite  should  be  proportioned  to  the  work 
to  be  done.  A  general  rule  applicable  to  all  explosives  is  :  That 
the  quantity  of  explosive  should  not  only  be  proportionate  to  the 
resistance,  but  the  hole  should  be  proportionate  to  the  explosive, 
or  the  explosive  to  the  hole. 

Tamping  dynamite  is  of  great  importance.  Mr.  Eissler 
says  that  it  is  a  fallacy  to  suppose  that  dynamite  "strikes  down- 
ward" more  than  upward,  and  that  tamping  is  thus  useless. 
By  reason  of  its  quickness  of  action  dynamite,  without  tamp- 
ing, will  do  much  work  where  gunpowder  would  do  nothing; 
but  the  former  will  do  much  more  effective  work  when  tamped. 
In  deep  and  down  holes  a  sufficient  amount  of  water  makes  a 
good  tamping,  but  sand,  brick  dust  or  clay  are  much  better.  A 
shallow  tamping  of  water  has  little  effect.  In  a  fissured  rock 
the  charge  should  be  surrounded  with  mud,  clay,  sand  or  water, 
when  possible.  In  tamping  dynamite  use  the  same  precaution 
for  putting  in  the  first  portion  of  the  tamping  as  specified  for 
black  powder. 

As  a  precautionary  measure,  it  is  well  to  push  a  ball  of  old 
newspaper  just  over  the  primer  and  under  the  tamping.  If 
the  shot  misses  fire  this  paper  will  indicate  the  nearness  of  the 
explosive,  in  removing  the  tamping  for  putting  in  another  car- 
tridge, as  before  described.  The  paper  also  prevents  the 
scraper  from  coming  in  contact  with  the  fulminating  cap. 

To  insure  effective  work  the  dynamite  must  not  be  frozen; 
the  fuse  must  be  good  and  properly  fitted  and  kept  in  the  cap ; 
the  cap  must  be  kept  dry,  and  must  not  be  withdrawn  from  the 
explosive. 


44  MODERN    TUNNEL    PRACTICE 

Dynamite,  as  a  rule,  throws  rock  less  and  breaks  it  more, 
and  extends  its  effects  much  deeper  than  ordinary  gunpowder. 
The  great  advantages  of  modern  explosives,  says  Mr.  Eissler, 
consist  not  so  much  in  diminishing  the  cost  of  explosives,  as  in 
increasing  the  amount  of  work  done.  The  difference  in  the  cost 
of  high  explosives  and  gunpowder  is  trifling  in  comparison 
with  the  difference  in  cost  of  drilling,  charging,  tamping,  con- 
venience in  wet  work  and  effectiveness  of  blasts. 

Effect  of  Nitroglycerine  Fumes. — The  best  account  of  the 
effect  of  nitroglycerine  fumes  upon  workmen  exposed  to  them 
is  probably  found  in  a  paper  presented  to  the  Medical  Rec- 
ord, in  1890,  by  Thomas  Darlington,  M.D.,  of  New  York. 
Dr.  Darlington  bases  his  article  upon  1,300  cases  of  asphyxia, 
partial  asphyxia  and  poisoning  resulting  from  the  product  of 
dynamite  combustion,  and  treated  by  him  during  the  construc- 
tion of  the  new  Croton  Aqueduct  for  New  York  City. 

He  divides  his  cases  into  two  classes ;  acute  cases,  where  the 
men  inhaled  considerable  quantities  of  the  gas  at  one  time ;  and 
chronic  cases,  where  the  men  constantly  breathed  a  small 
amount  of  the  gases.  In  the  acute  cases,  the  symptoms  are : 
giddiness,  a  trembling  sensation,  frequently  nausea,  sometimes 
vomiting,  a  fullness  in  the  head,  and  intense  headache;  the 
heart's  action  is  increased  and  the  pulse  is  full  and  round.  If 
the  man  is  brought  into  sudden  contact  with  a  large  percentage 
of  the  poisonous  fumes — as  just  after  a  blast — the  giddiness  is 
immediately  followed  by  unconsciousness,  and  the  patient  pre- 
sents the  usual  appearance  of  asphyxia.  The  comatose  condi- 
tion soon  passes  away  and  is  succeeded  by  drowsiness,  languor, 
cold  perspiration,  intermittent  pulse,  and  generally  nausea  and 
vomiting.  Nearly  all  the  cases  mentioned  recovered,  no  matter 
how  serious  they  seemed  at  the  time. 

In  the  chronic  cases  the  four  prominent  symptoms  are :  head- 
ache, cough,  indigestion,  and  disturbance  of  the  nervous  system. 
The  cough  is  similar  in  character  to  that  of  pertussis,  or  ma- 
laria. In  nearly  all  cases  there  is  a  continuing  headache  and 
neuralgia.  As  soon  as  the  patient  is  removed  from  the  tunnel 
and  put  to  work  above  ground,  he  steadily  improves  and  will 


BLASTING  45 

finally  recover  entirely.  Men  who  previously  suffered  from 
dyspepsia  or  neuralgia  are  made  much  worse  by  dynamite 
smoke. 

In  treating  these  cases,  Dr.  Darlington  proceeded  as  in  cases 
of  asphyxia,  adding  to  this  treatment  cold  applications  to  the 
head;  and  he  administered  subcutaneously  atropine,  ergotme, 
or  other  vaso-motor  stimulants.  He  recommends  that  work- 
men carry  small  vials  of  aromatic  spirits  of  ammonia  for  imme- 
diate use,  in  case  of  necessity,  as  he  believes  that  a  nitrate  is 
formed  in  the  blood  from  the  decomposition  of  nitroglycerine. 
The  inhaling  of  ammonia  also  has  a  beneficial  effect. 

Hints  in  Power  Drilling. — In  seamy  rock,  drills  mounted  on  a 
bar  are  apt  to  bind  in  a  hole,  and  much  time  is  lost  in  pounding 
them  loose.  Instead  of  discarding  the  power  for  a  hand-drill, 
some  miners  advise  the  use  of  the  tripod  as  a  mounting  in  such 
cases.  The  whole  machine  can  then  be  moved  slightly  by  rais- 
ing or  lowering  one  of  the  legs,  and  the  trouble  due  to  binding 
is  entirely  done  away  with. 

In  overhead  stoping,  however,  a  tripod  cannot  be  so  readily 
set  up  or  moved,  because  of  the  irregularity  of  the  broken  rock 
on,  which  it  stands.  But  in  such  case  a  rough  platform  of  lag- 
ging can  be  used  to  advantage.  Or  a  small  wooden  triangle 
answers  even  better  than  the  platform,  as  it  holds  the  tripod 
and  is  readily  blocked  up. 

To  facilitate  drilling  in  seamy  ground  it  is  recommended  to 
make  the  short  bits,  used  first,  larger  in  diameter  than  the  long 
ones.  And  another  expedient  is  to  use  drills  having  four 
shoulders  or  wings,  extending  6  or  8  inches  up  the  drill-shank 
from  the  cutting  edge,  and  only  a  trifle  less  in  diameter  than 
the  drill.  These  wings  check  the  tendency  of  the  cutting  edge 
to  follow  the  slant  of  a  seam. 

To  Prevent  Crushing  of  Shaft  Timbers  by  Blasting. — Mr.  C.  K. 
Colvin,  M.  E.,  of  Denver,  Colo.,  describes  a  "float,"  or  a  device 
used  to  prevent  the  crushing  of  the  bottom  timbering  of  a  shaft 
by  blasts.  This  consists  of  two  thicknesses  of  i-inch  boards 
laid  crosswise  and  faced  on  each  side  with  ^-inch  boiler-iron, 
well  bolted. 


46  MODERN    TUNNEL    PRACTICE 

The  wood  center  acts  as  a  cushion  to  protect  the  plates.  This 
float  is  built  at  the  bottom  of  the  shaft,  and  is  large  enough  to 
extend  at  least  2  inches  beyond  the  timbers.  It  is  supported  at 
the  four  corners  by  2-ton  chain  blocks,  and  just  before  firing  it 
is  pulled  up  tight  against  the  bottom  timbers.  There  is  a 
"bucket-hole"  through  the  center  of  the  float  and  this  is  closed 
by  a  chain  net.  After  some  months'  use  the  float  is  usually 
battered  into  a  cup  shape ;  it  is  then  turned  over  so  that  it  will 
be  battered  back  again. 


CHAPTER  IV 

SHAFT-SINKING 

Location  of  shafts — Dimensions — Relation  of  shaft-work  to  tunneling 
proper — General  conditions  of  shaft-sinking — Forces  exerted  on  tim- 
bers and  precautions  to  be  observed — Steel  shaft-house — Cages  and 
skips — Cheap  form  of  hoisting-cage  and  head-house — Shaft-sinking  in 
wet  gravel  and  quicksand — Sheet-piling  shaft. 

At  the  present  time  shaft-sinking  is  largely  confined  to  the 
extraction  of  minerals  of  various  kinds  and  to  the  exploitation 
of  city  subways,  or  subaqueous  tunnels.  In  the  days  of  black 
powder  and  hand-drilling,  shafts  were  sunk  at  frequent  inter- 
vals on  railway  tunnels  of  any  considerable  length,  for  the  pur- 
pose of  providing  a  greater  number  of  working  faces  and  thus 
hastening  the  completion  of  the  work.  The  use  of  high  explo- 
sives, power  drills  and  improved  machinery  for  removing  the 
debris  have  so  increased  the  rate  of  progress  in  tunneling  work 
that  the  old-time  necessity  for  a  number  of  shafts  has  largely 
disappeared. 

Location  of  the  Shaft. — Where  a  shaft  is  necessary  it  may  be 
located  directly  upon  the  center  line,  or  to  one  side  and  outside 
the  width  of  the  tunnel.  In  the  United  States  the  former  posi- 
tion is  very  generally  preferred.  The  shaft  on  the  center  line  is 
better  adapted  to  transferring  the  alignment  to  the  tunnel 
below;  it  is  more  convenient  for  the  laying  of  track  and  the 
handling  of  cars  at  the  foot  of  the  shaft ;  and  the  center  shaft 
costs  less  than  one  for  which  a  cross-cut  has  to  be  made.  In 
treacherous  soil  the  side  shaft  may  also  bring  about  a  disturb- 
ance of  the  material  at  the  side  of  the  tunnel  and  lead  to  a 
dangerous  slip. 

Dimensions. — The  horizontal  dimensions  of  a  shaft  must  be 
carefully  proportioned  to  the  character  and  amount  of  material 
to  be  hoisted,  and  to  the  pumping  and  ventilating  plant  that 

47 


48  MODERN    TUNNEL    PRACTICE 

may  possibly  be  needed.  A  shaft  that  is  too  small  for  the  work 
proposed  is  an  endless  source  of  trouble  and  expense,  for  the 
shaft  is  the  neck  of  the  bottle  through  which  everything  must 
pass  in  and  out,  and  its  dimensions  are  thus  the  controlling 
factor. 

The  usual  shaft  is  rectangular  in  plan  and  nearly  twice  as 
long  as  it  is  wide.  This  form  permits  of  the  establishment  of 
separate  compartments  for  hoisting  and  for  the  pumping  and 
ventilating  pipes,  and  provides  means  for  the  constant  inspec- 
tion and  repair  of  the  pipe  system  without  interfering  with  the 
regular  hoisting  work.  Unless  the  shaft  is  a  permanent  one 
ladders  or  a  stairway  are  seldom  provided.  Square  or  circular 
shafts  are  badly  adapted  to  the  disposition  of  the  plant. 

Shaft  Sinking. — Owing  to  its  vertical  or  sharply  inclined 
position  and  the  consequent  collection  of  water  on  the  bottom, 
or  working  face ;  to  its  limited  dimensions ;  to  the  extraction  of 
the  material  by  a  bucket-hoist,  and  to  the  necessary  shifting  of 
pumps  and  pipes,  competent  authorities  estimate  that  it  re- 
quires, from  1 5  to  20%  more  time  to  sink  a  shaft  per  lineal  foot 
of  advance  than  to  drive  a  tunnel  heading  of  similar  dimen- 
sions. The  cost  is  also  much  greater  owing  to  the  conditions 
cited. 

The  method  adopted  for  sinking  any  shaft  depends  entirely 
upon  the  character  of  the  material  to  be  penetrated.  If  this 
material  is  fairly  solid  and  homogeneous  rock,  with  little  water, 
the  task  is  a  comparatively  simple  one.  But  if  the  material  is 
water-bearing,  is  soft  or  liable  to  run  into  the  bottom  of  the 
shaft  as  it  is  being  excavated,  it  is  only  a  question,  of  time 
when  the  ground  about  the  shaft  will  be  "moving"  and  exerting 
unequal  and  destructive  pressures  upon  the  shaft  timbering, 
tending  to  tear  these  timbers  apart  vertically.  Every  precau- 
tion must  be  taken  to  prevent  this  movement  in  the  adjacent 
soil  by  careful  timbering,  and  by  floors,  if  the  soil  is  very  soft. 
In  very  bad  soil  iron  cylinders  are  sometimes  employed,  either 
sunk  in  solid  rings  added  from  above  and  forced  down,  or  by 
segmental  rings  bolted  into  place  at  the  bottom. 

In  loose  or  running  ground,  with  any  system  of  timbering 


SHAFT-SINKING  49 

that  may  be  adopted,  the  important  precautions  to  be  observed 
by  the  timber-men  are  the  following :  Make  the  timbers  heavy 
enough  to  resist  all  lateral  pressures.  To  guard  against  the 
horizontal  separation  of  the  sets,  or  timbers,  see  that  these  sets 
are  securely  tied  together  vertically,  thus  anchoring  them  to 
timbers  on  firm  ground  above — if  such  ground  exists ;  and  in 
any  event,  hang  the  timber  together  as  the  shaft  is  built  down- 
ward. Above  all,  prevent,  if  possible,  the  removal  of  any 
ground  outside  the  cube  of  the  shaft  itself ;  any  space  thus  left 
outside  the  timbers  by  careless  excavation  will  be  filled  up  by 
pressure  from  above  and  gradually  start  a  dangerous  movement 
in  the  soil  about  the  shaft.  In  very  soft  ground  the  material  in 
the  bottom  may  have  a  tendency  to  swell,  or  "rise"  in  the  shaft. 
This  is  an  exceedingly  troublesome  problem  to  deal  with,  and  is 
overcome  usually  by  flooring  the  bottom  of  the  shaft  and 
strongly  bracing  from  above,  and  sinking  this  floor  in  sections 
made  as  small  as  possible.  As  a  rule,  in  bad  ground,  all  open- 
ings made  in  the  sides  for  new  timbers,  or  in  the  bottom  for 
sinking,  should  be  so  small  as  to  be  always  under  control,  care- 
fully "poling"  the  space  to  be  finally  provided  for  a  new  timber, 
in  such  manner  as  to  prevent  a  "run"  of  soil  from  without. 

In  sinking  a  shaft  or  in  driving  a  tunnel  too  much  stress  can- 
not be  laid  upon  the  importance  of  adhering  as  closely  as  possi- 
ble to  the  true  section  of  the  excavation.  As  remarked  before, 
voids  outside  this  section  inevitably  invite  and  bring  about  pres- 
sure, and  the  final  amount  of  this  stress  cannot  be  even  esti- 
mated. If  such  voids  are  unavoidable,  as  is  often  the  case  in 
tunnel  driving,  they  should  be  carefully  and  completely  filled  by 
masonry  or  by  packing  of  loose  stone.  And  it  is  the  duty  of  the 
engineer  to  see  that  this  is  done.  With  the  purpose  of  hasten- 
ing the  completion  of  a  certain  piece  of  masonry  careless  work- 
men are  too  prone  to  scamp  this  packing,  with  the  impression 
that  it  will  never  be  discovered.  This  is  especially  the  case  in 
tunnel  lining ;  and  the  writer  has  personally  known  cases  where 
a  man  could  stand  upright  in  the  space  left  over  a  tunnel  arch, 
and  where  empty  cement  barrels  were  substituted  for  the  stone 
packing  called  for  in  the  specifications.  As  a  matter  of  fact, 


50  MODERN    TUNNEL    PRACTICE 

few  tunnel  linings  fail  under  direct  pressure  upon  this  lining; 
in  nearly  all  cases  failure  can  be  directly  traced  to  unfilled  voids. 

Various  methods  are  employed  for  sinking  a  shaft  through 
sand  or  other  water-bearing  material  of  a  comparatively  homo- 
geneous nature;  and  some  of  these  methods  are  described  in 
more  detail  in  succeeding  pages.  Among  these  methods  may  be 
noted  the  plenum  pneumatic,  or  compressed-air  process,  oper- 
ated either  in  iron  cylinders  bolted  together  by  horizontal 
flanges,  or  in  caissons  connected  with  the  part  above  the  water 
level  by  cylindrical  shafts.  The  use  of  compressed  air  in  this 
connection  is  practically  limited  to  a  depth  of  about  no  feet, 
by  its  effect  upon  the  human  organism,  and  it  is  generally  em- 
ployed in  foundation  work  for  piers  in  bridges  or  building 
construction. 

The  freezing  process  is  employed  under  circumstances  which 
warrant  the  necessary  expenditure,  in  sinking  a  shaft  through 
wrater-bearing  material.  In  this  process  the  ground  and  the 
contained  water  is  frozen  to  a  solid  mass  for  some  distance  out- 
side the  limits  of  the  shaft,  by  first  sinking  vertically  a  circle 
of  special  double  pipes,  penetrating  to  the  full  depth  of  the  pro- 
posed shaft,  and  then  circulating  through  these  pipes  brine  or 
other  freezing  compounds.  When  the  ground  is  sufficiently 
solid  the  shaft  is  excavated  and  lined  in  the  usual  manner. 
This  process  is  described  in  more  detail  in  a  following  portion 
of  this  book. 

The  Kind-Chaudron  method  of  shaft-sinking  had  its  origin 
in  Belgium  and  has  had  a  limited  use  in  sinking  shafts  in  the 
coal  regions  of  that  country.  Briefly  stated,  the  process  con- 
sists in  sinking  iron  cylinders  by  using  heavy  and  specially  de- 
vised cutters  for  breaking  tin  the  bottom  material ;  these  being 
operated  from  the  top  of  the  shaft  and  through  any  depth  of 
water  in  the  shaft.  The  material  thus  broken  up  is  removed  by 
dredging  through  the  water,  and  as  the  cylinder  sinks,  its 
length  is  increased  by  adding  sections  at  the  top.  It  is  an  ex- 
pensive method,  slow  in  operation,  and  is  liable  to  fail  from  the 
difficulty  of  keeping  the  cylinder  in  a  vertical  line,  and  its  con- 
sequent jamming. 


SHAFT-SINKING 


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52  MODERN    TUNNEL    PRACTICE 

In  his  monumental  work  on  tunneling*  Mr.  Drinker  gives 
the  following  general  precautions  to  be  observed  in  sinking  a 
shaft  through  treacherous  ground.  These  precautions  amplify 
some  of  the  remarks  made  above. 

1.  Regular  and  constant  examination  of  the  shaft-timbering ; 
so  that  all  wedges,  bolts,  props,  joints,  etc.,  may  be  kept  tight. 

2.  All  holes  must  be  quickly  stopped,  and  even  small  cracks 
should  be  at  once  plugged  with  straw  or  similar  material. 

3.  Careful,  tight  connection  must  be  maintained  between 
the  inner  and  outer  timbering.    If  wedging  does  not  suffice,  use 
props,  or  spikes  and  clamps. 

4.  Where  there  is  wrenching  and  distortion,  connect  the  sets 
by  longitudinal  "bars,"  or  put  in  rakers  or  bearing  beams,  when 
the  ground  at  the  bottom  of  the  shaft  is  solid  enough  for  this 
purpose. 

5.  Do  not  forget  that  all  pressure  is  intensified  by  neglect, 
and  that  this  pressure  tends  to  increase  in  considerably  more 
than  a  direct  proportion. 

After  a  shaft  is  sunk  to  the  tunnel  or  mine  level,  it  must  be 
operated;  and  for  this  purpose  a  hoisting  plant  is  necessary, 
proportioned  according  to  the  amount  of  hoisting  work  to  be 
performed  and  the  temporary  or  permanent  character  of  the 
work  itself.  The  shaft-house,  or  head-house,  contains  the  steam- 
generating  plant,  the  hoisting  engines,  drying-rooms,  etc. ;  and 
the  head  of  the  shaft  must  be  equipped  with  the  proper  railway 
tracks  leading  to  the  dumping  ground,  or  to  storage  or  load- 
ing bins. 

A  Simple  Hoisting  Cage. — The  tunnel  elevator,  or  cage,  here 
illustrated  is  intended  to  show  a  cheap  and  easily  constructed 
hoisting  appliance  that  has  been  thoroughly  tested  by  long  and 
hard  service.  In  the  particular  case  referred  to,  the  timber 
used  in  its  construction  was  hard  pine,  though  other  strong 
wood  can  be  employed.  It  was  entirely  made  upon  the  works, 
and  its  detail  and  dimensions  are  fully  shown  in  Fig.  10. 

The  shaft-guides  were  4  x  4-inch  yellow  pine  sticks,  planed 

*"Tunneling,  Explosive  Compounds  and  Rock  Drills,"  by  Henry  S. 
Drinker,  E.M. ;  New  York,  1878,  John  Wiley  &  Sons. 


SHAFT-SINKING  53 

on  three  sides  and  secured  by  f-inch  counter-sunk  bolts  to  a 
4  x  lo-inch  timber  as  shown.  These  guides  were  kept  well  oiled. 
The  safety  appliance  was  made  of  a  pair  of  steel-pointed  chisel- 
arms,  secured  at  the  elbow  by  a  i^-inch  pin  passing  through 
the  uprights  of  the  cage ;  and  these  pins  practically  carried  the 
whole  weight  of  the  cage  and  its  load.  On  the  bottom  of  the 
cross-head  of  the  cage  frame  an  iron  plate,  ^-inch  thick,  was 
secured;  and  against  this  plate  reacted  a  strong,  three-leaf 
spring,  passing  through  the  bottom  of  the  bar  carrying  the 
hoisting  rope.  The  inside  ends  of  the  chisel-bars  worked  in 
a  box  secured  to  the  bottom  of  this  suspension-bar.  The  spring 
was  adjusted  so  as  to  resist  the  weight  of  the  empty  cage ;  and 
so  long  as  the  hoisting  rope  was  intact  the  vertical  part  of 
the  chisel-arm  lay  inside  the  socket  provided  in  the  uprights. 
But,  should  the  rope  break  from  any  cause,  the  spring  was  re- 
leased, and  the  horizontal  arm  was  pushed  downward  by  it; 
the  vertical  or  chisel-arm  was  thus  pushed  outward  and  into  a 
position  to  cut  into  the  4  x  4-inch  guide  member  as  the  cage  de- 
scended. In  this  particular  cage  the  safety  device  was  severely 
tested  several  times  by  the  breaking  of  the  hoisting  rope,  with 
a  full  load  on  the  cage.  In  each  case  the  cage  was  brought  to 
a  standstill  with  a  maximum  fall  of  20  inches ;  the  guides  were 
badly  cut  up  in  the  operation,  but  their  construction  permitted 
the  rapid  replacement  of  the  damaged  portion. 

The  "cage-stop,"  for  holding  in  adjustment  the  platform 
track  and  the  track  leading  to  the  dump,  was  effective  and  eas- 
ily handled.  The  cage  in  ascending  opened  the  stops ;  and  these 
fell-  into  place  by  gravity  as  the  cage  passed  through  them. 
In  sending  the  cage  down,  the  latter  was  hoisted  a  little,  and 
the  stops  were  thrown  back  and  out  of  its  way  by  the  hand- 
lever  shown. 

As  an  open  shaft-mouth  is  a  source  of  frequent  danger  to 
the  top-men,  this  shaft  was  always  closed  at  the  top,  either  by 
the  cage  itself  or  by  a  grillage  made  as  shown.  This  grillage 
was  long  enough  to  extend  over  the  sides  of  the  opening 
and  strong  enough  to  support  a  car.  When  the  cage  came 
up  it  lifted  the  grillage  with  it  on  the  cross-head  of  the 


54 


MODERN    TUNNEL    PRACTICE 


cage.  The  hoisting  frame  is  sufficiently  well  shown  in  the 
illustration. 

Steel  Shaft-house.— During  1902  the  Oliver  Iron  Mining 
Company,  of  Duluth,  Minn.,  put  down  two  shafts  at  Ely, 
Minn.,  1,500  feet  apart,  but  both  operated  by  a  single  hoisting 
plant.  As  the  house  at  each  shaft  is  constructed  of  steel,  a 
brief  description  of  the  plant  is  here  given,  as  showing  the  latest 
practice  in  this  direction.* 

The  shaft-house  here  shown  (Figs,  n  and  na)  was  built  by 
the  American  Bridge  Company  at  its  Minneapolis  shops,  and 
is  30  feet  wide  on  the  face,  75  feet  deep  on  the  ground  level, 


FIG.  na. —   Foundation  Plan  of  Steel  Shaft-house,  Ely,  Minn. 

and  is  158  feet  high  from  the  collar  of  the  shaft.     About  265 
tons  of  structural  steel  were  used  in  its  erection. 

The  main  frame  is  made  of  columns  composed  of  pairs  of 
steel  channels,  with  horizontal  lines  of  steel  channel-framing  be- 
tween them.  As  it  is  not  advisable  to  build  column  foundations 
close  to  the  shaft,  the  first  columns  are  supported  on  a  heavy 
box  girder.  The  two  heavy,  inclined  columns  at  the  rear  of  the 

*For  a  detailed  description  of  this  plant,  by  Mr.  Frank  Drake,  M.  Am. 
Inst.  M.  E.,  Chief  Engineer  of  the  company,  see  Engineering  News,  Nov. 
19,  1903. 


SHAFT-SINKING 


55 


house  act  as  braces  to  resist  the  pull  of  the  hoisting  ropes, 
which  pass  over  the  1 2-inch  grooved  sheaves  near  the  top  of 
the  house.  At  a  height  of  33  feet  above. the  shaft  is  a  projec- 


Half   front  Elevation.        .'  Half  Reor  ElevOT 


FIG.  ii. — Steel  Shaft-house:  Oliver  Iron  Mining  Co.,  Ely,  Minn. 


tion  enclosing  the  guides  and  cages,  this  projection  being  sup- 
ported by  cantilever  girders  with  latticed  webs.  At  the  level 
of  the  first  floor  is  a  line  of  36-inch  plate-girders  and  lattice-. 


MODERN    TUNNEL    PRACTICE 


girders  between  the  outer  columns,  instead  of  the  1 5-inch  chan- 
nels between  the  inner  columns,  as  shown  in  the  section. 

The  fine  and  lump  ores  are  dumped  from  the  cages  through 
separate  hoppers  into  bins;  from  the  latter  it  is  discharged  as 


Front    Elevation. 


FIG.  12.— Cage  for  Sibley  Shaft :    Oliver  Iron  Mining  Co.,  Ely,  Minn. 


required  into  cars  standing  on  tracks  which  pass  through  the 
shaft-house.  These  hoppers  are  made  of  5-16  inch  steel  plate; 
while  the  bins  have  plank  lining  attached  to  the  structural 
framework.  The  whole  shaft-house  is  sheathed  with  corru- 


SHAFT-SINKING 


57 


gated  steel,  painted  with  two  coats  of  iron-ore  paint  on  all  its 
members,  excepting  only  the  interior  of  the  hoppers  and  the 
lining  woodwork. 

Cages  and  Skips.— As  one  shaft  is  vertical  and  the  other  in- 
clined, the  cages  and  skips  used  differ  in  design ;  and  both  types 
are  here  shown  in  all  their  dimensions.  All  of  the  structural 
material  is  soft,  open-hearth  steel ;  the  floor  is  2-inch  plank  cov- 
ered with  ^-inch  steel  plate.  The  two  draw-bar  springs  are 


.  .^_ 


FIG.  I2a.— Skip  Used  in  the  Sibley  Shaft. 


made  of  square  steel,  and  they  have  an  outside  diameter  of  6^ 
inches,  and  a  length  of  7  inches  when  free.  Under  10,000 
pounds  load  the  compression  is  ij  inches. 

The  skip  for  the  vertical  shaft  weighs  4,678  pounds,  or  4,935 
pounds  with  a  lip.  The  construction  is  plainly  shown  in  the 
illustrations. 

Shaft-sinking  in  Wet  Gravel  and  Quicksand. — The  Penn  Min- 
ing Company,  of  Norway,  Mich.,  in  1890  found  it  necessary 
to  sink  a  shaft  through  60  feet  of  glacial  drift  very  heavily 


50  MODERN    TUNNEL    PRACTICE 

charged  with  water.    It  was  decided  to  sink  a  caisson,  or  drop- 
shaft,  to  reach  the  underlying  impermeable  stratum. 

The  top  of  the  shaft  (Fig.  14)  was  6x  13  feet  inside;  the 
bottom  was  made  4  feet  larger  each  way,  or  lox  17  feet  in- 
side; and  to  within.  12  feet  of  the  bottom  the  shaft  was  divided 
into  three  compartments,  the  middle  one  being  uniformly  4  feet 


•Anachmenr  TO  Cage 


I 


A 

\.     j. 

•» 

v    &    "    "    ~     " 
Front   Elevation. 

yfaaanr  1  1° 

|  '*  i  n 

Ii        .  i  i, 

^: 

|j 

g 
^ 

Bottom       Plan 


ife 


Side     Elevation  Ntws. 


Section  of  Guide  Shoe 
on  Line  A- B. 


FIG.  13.  —  Skip  for  Savoy  Shaft. 

wide.  As  shown  in  Fig.  15,  the  pumps  were  placed  in  the  two 
end  compartments,  and  these  were  covered  over  to  admit  of 
sand  for  loading  the  caisson.  The  middle  compartment  was 
used  for  hoisting,  the  pipes,  etc.  A  ventilating  box  was  put 
in  one  corner  of  the  shaft. 


SHAFT-SINKING 


59 


The  bottom  timbers  of  the  shaft  were  oak,  15  inches  square, 
beveled  to  6  inches.  Above  these  came  white  pine  sticks  12 
inches  square,  framed  in  sets  and  bolted  together  and  to  the 
shoe  with  eight  bolts  each  5  feet  long.  The  successive  sets 
were  reduced  i  inch  in  width  and  length,  until  at  48  feet  above 
the  bottom  the  dimensions  corresponded  with  the  top  set.  The 
corner-posts  were  12  inches  square,  and  broke  joints  with  each 
other.  They  were  bolted  to  every  other  side  and  end  piece. 
The  bolts  were  put  in  from  the  inside,  with  the  nuts  counter- 
sunk; they  were  thus  easily  recovered  when  the  corner-posts 
were  removed.  The  side-posts  were  secured  in  a  similar  man- 


4..-.  v  — • 

,8'.... 


FIG.  14. —  Top  and  Bottom  Sets:  Harrison  Shaft,  Norway,  Mich. 

ner,  one  at  each  corner  of  the  middle  compartment.  At  every 
5  feet  12-inch  dividers  were  used. 

After  the  ground  had  been  leveled  the  caisson  was  built  up 
and  bolted  to  a  height  of  about  30  feet.  The  seams  were  care- 
fully caulked  outside,  and  3-inch  plank  was  spiked  on  vertically 
to  protect  the 'caulking  and  still  further  strengthen  the  caisson. 
Steam  hose,  and  later  elbowed  pipe,  were  used  to  connect  the 
pump  with  the  boilers. 

The  quantity  of  water  to  be  pumped  was  estimated  at  1,500 
gallons  a  minute ;  and  this  water  was  charged  with  fine,  sharp 
sand,  that  rapidly  wore  out  the  pump-linings,  causing  delay. 
The  shaft  was  sunk  the  60  feet  in  sixty-three  days,  including 
all  delays. 

The  flow  of  water  at  the  bottom  was  stopped  as  follows: 
The  corner-posts  were  taken  out,  the  bolt-holes  were  plugged, 


6o 


MODERN    TUNNEL    PRACTICE 


and  the  inside  of  the  shaft  was  caulked.  Then  the  shaft  was 
sunk  1 1  feet  into  the  ledge.  To  seal  the  bottom  of  the  drop- 
shaft,  a  set  of  12  xi  2-inch  timbers,  6x13  feet  inside,  was 
carefully  placed  in  line  with  the  top  set,  as  shown  in  Fig.  16, 
and  extending  about  6J  feet  below  the  shoe.  This  set  was 


FIG.  15. — Harrison  Shaft:  Longitudinal  Section. 

thoroughly  blocked  against  the  rock  by  wedges,  and  six  other 
sets  were  built  upon  it,  each  being  bolted  to  the  one  below.  A 
thin  layer  of  clay  was  put  over  the  wedges,  and,  as  the  suc- 
cessive sets  were  put  in,  a  concrete  of  equal  parts  of  sand  and 
cement  was  packed  between  the  timbers  and  the  rock. 
Through  the  top  set,  which  was  about  on  the  level  of  the  shoe, 


SHAFT-SINKING 


6l 


twenty  2-inch  holes  had  been  bored ;  and  behind  these  holes  was 
laid  a  4-inch  layer  of  broken  stone.  Three  other  sets  were  laid 
on  this  last  set,  gradually  widening  out,  with  the  top  set  bolted 
to  the  sides  of  the  caisson.  The  space  behind  these  was  also 
filled  with  concrete,  and  this  was  allowed  to  set.  The  holes 


FIG.  16. — Method  of  Closing  the  Bottom  of  the  Harrison  Shaft,  Norway, 

Michigan. 

in  the  special  set  were  finally  plugged,  and  the  inflow  of  water 
at  once  dropped  to  200  gallons  per  minute.  Thorough  inside 
caulking  further  reduced  this  flow  to  90  gallons. 

Sheet-piling  Shaft.*— The  Brooklyn  shafts  for  the  extension 

*For  a  detailed  description  of  this  work  see  Engineering  Record,  Oct. 
3i,  1903- 


62 


MODERN    TUNNEL    PRACTICE 


of  the  New  York  Rapid  Transit  Railway  under  the  East  River 
are  made  of  sheet-piling,  as  here  shown.  The  two  shafts  are 
50  feet  apart  on  centers,  and  each  one  is  23  feet  1 1  inches  by  20 
feet  2  inches  in  inside  dimensions,  and  is  65  feet  deep.  The  ma- 
terial penetrated  is  as  follows:  Ten  feet  of  loam,  35  feet  of 
boulders  and  gravel,  and  the  remainder  is  in  sharp,  fine  sand 
that  runs  quite  freely.  The  water  level  is  about  60  feet  below 
the  street  surface. 

The  shafts  (Fig.  17)  were  sunk  by  open  excavation  inside 
sheet  piling  driven  down  as  the  work  progressed.     An  outer 


vertical  Boards  M'Lbncf  . 


Plon   of  Shof*  Timbering 


Section  thr 


FIG.   17.—  Sheet-piling  shaft:  New  York  Rapid  Transit  Railway,  Brook- 

lyn Extension. 

guide  frame  of  12  x  1  2-inch  timbers  was  first-  laid  down  on 
the  ground;  and  inside  of  this  were  placed  the  12  x  1  2-inch 
rangers,  braced  as  shown.  In  the  4-inch  space  between  these 
sets  the  4  x  lo-inch  tongued  and  grooved  braced  sheet-piling 
was  driven.  These  piles  were  cut  at  the  lower  end  to  an  angle 
of  60°,  and  shod  with  a  thin,  bent  steel  plate  7  inches  wide. 

The  sheet-piling  was  driven  by  a  steam  hammer,  commencing 
at  one  corner  of  the  shaft  and  driving  successively  around  the 
four  sides,  driving  each  pile  uniformly  one  to  two  feet  at  a 
time.  A  gang  of  ten  men,  working  ten  hours  per  day.  exca- 
vated 15  feet  of  shaft  in  one  week. 

The  sheet-piling  was  65  feet  long;  and  each  pile  was  made 


SHAFT-SINKING 


In  five  sections  with  a  halved  butt  and  lap-joint,  each  joint 
secured  by  eight  or  more  5-inch  wire  nails.  The  excavation 
was  kept  just  above  the  bottom  of  the  sheeting.  The  corner 
sheeting  was  dovetailed  and  bolted  together,  and  driven  as  one 
pile.  The  bottom  ranger  set  was  braced  up  horizontally  from 


ta    z 


i  \u  _ 


Sheet  Pile  Driver,  suspended    from   Derrick   Boom. 

PiG.  I7a. — Device  for  Cushioning  the  Blow  of  the  Hammer  on  Sheet-piling. 

the  bottom  of  the  pit,  while  the  piles  were  driven  against  it. 
After  the  excavation  had  been  carried  about  2  feet  below  this 
set  a  second  ranger  set  was  put  together  at  the  bottom  of  the 
pit,  and  lo-ton  hydraulic  jacks  were  set  up  at  each  corner  of 
the  shaft  reacting  upon  the  frame  above.  As  the  digging  pro- 
ceeded these  jacks  drove  the  bottom  set  downward,  and  this 


64 


MODERN    TUNNEL    PRACTICE 


was  continued  until  there  was  a  space  of  6  feet  between  the 
sets.  The  upper  frame  was  now  temporarily  supported  on 
cleats  nailed  to  sheeting,  and  the  jacks  were  removed.  Dig- 
ging was  resumed,  and  as  soon  as  2  feet  had  been  gained 
the  above  operation  was  repeated.  The  ranger  sets  were  hung 
to  each  other  by  a  pair  of  vertical  planks  nailed  in  each  corner. 
The  pile-driver  had  special  wooden  leads,  made  as  shown 


FIG.  18.— Plan  and  Elevation  of  Shaft  at  Aspen  Tunnel. 

(Fig.  173),  and  arranged  in  such  manner  that  the  2,ooo-pound 
hammer  struck  this  wooden  packing  and  thoroughly  drove 
the  piles. 

The  accompanying  illustration  (Fig.  18)  shows  the  method 
adopted  for  timbering  a  shaft  on  the  Aspen  tunnel  of  the  Union 
Pacific  Railway.  This  shaft  was  331  feet  deep,  and  penetrated 
hard  but  seamy  sandstone,  carrying  very  much  water  below  the 
257-foot  level. 


CHAPTER    V 

PRINCIPLES   OF   TUNNEL   TIMBERING   AND   DRIVING 

General  rules — Choice  of  timber — English  method  of  timbering  as  applied 
in  the  United  States — Belgian  and  Belgian-German  system — German 
system — Austrian  system — American  system — Driving  through  loose 
gravel — Crutch  system — Timbering  a  sand  tunnel — Meem  paling-board 
system — Iron  crown-bar  system — Old  rail  crown-bars,  their  advantages 
and  disadvantages — Steel-lined,  tunnel — Sand-chamber  and  caisson 
method — Pilot-tunnel  system — Sewer  tunnel  in  quicksand — Dry-sand 
tunneling — Enlarging  tunnel  in  soft  ground — Sewer  tunnel  in  dry  sand. 

The  particular  manner  of  timbering  a  tunnel  will  depend 
upon  the  nature  of  the  material  and  the  experience  and  choice 
of  the  miner  conducting  the  work.  But  some  of  the  funda- 
mental principles  underlying  work  of  this  character  may  be 
noted  as  follows : 

Compression  is  very  largely  the  force  against  which  the 
miner  has  to  contend.  Therefore,  all  joints  should  be  of  the 
simplest  character,  as  all  notching,  mortising,  dovetailing,  etc.. 
tends  to  weaken  and  split  timbers  under  pressure;  and  where 
angles  are  necessary  flat  surfaces  and  wide  angles  only  can  be 
used  with  any  safety  for  abutting  timbers.  The  pressure  itself 
tends  to  tighten  the  joints ;  and,  to  avoid  slipping,  heavy  spikes 
driven  outside  of  the  upright  timbers  are  most  satisfactory. 

In  nearly  every  system  of  timbering,  wedges  are  an  important 
factor  in  securing  tightness  between  surfaces.  Wedges  are  em- 
ployed to  tighten  joints  and  to  lengthen  timbers  that  are  too 
short ;  and  as  they  may  be  cut  out,  they  permit  the  removal  of 
timbers  in  heavy  ground  and  under  pressure. 

As  a  rule,  spikes  and  nails  should  not  be  driven  into  the 
timbering  proper,  the  one  exception  being  the  heavy  spikes,  or 
"brobs,"  referred  to  above,  to  keep  the  foot  of  a  post  from 
slipping,  or  the  top  of  a  post  from  coming  out  from  under  a 

65 


66 


MODERN    TUNNEL    PRACTICE 


cap.  But  in  both  of  these  cases  the  spikes  are  driven  outside 
of  the  post  or  strut,  and  not  into  it.  A  great  part  of  the  tim- 
bering used  in  a  tunnel  must  come  down  again,  and  it  may  be 
essential  to  remove  it  as  quickly  as  possible.  Hence,  any  spik- 
ing of  timbers  delays  and  makes  more  difficult  the  work  of 
removal  or  shifting.  Screw-bolts  are  made  to  fasten  together 


English  System. 


Belgian  System. 


German  System. 


Austrian  System. 


FIG.    i8a. — Diagrams    Illustrating    Four    Systems    of   Tunnel    Attack;    the 
Numerals  Showing  the  General  Sequence  of  Excavation. 

the  segments  of  arch-centering,  in  making  fish- joints,  etc.,  but 
these  are  easily  removed.  Where  the  risk  will  warrant  the 
cost,  rings  or  bands  may  be  employed  to  prevent  timbers  from 
splitting ;  and  in  shaft-sinking,  iron  hangers,  heavy  steel  cables 
or  tie-rods  may  be  necessary  to  hold  the  sets  together  vertically. 


PRINCIPLES  OF  TUNNEL  TIMBERING  AND  DRIVING  67 

Another  very  useful  appliance  in  tunnel-timbering  is  a  screw- 
jack  fastened  to  one  end  of  a  heavy  timber.  These  jack-timbers 
save  time,  and  are  economical  of  timber  in  special  cases ;  and 
as  they  are  quickly  adjusted  to  length  and  applied,  they  may 
be  very  useful  in  an  emergency.  - 

Tunnel-timbering  is  a  temporary  means  of  supporting  the 
roof  or  sides  until  the  tunnel  section  can  be  excavated  and  the 
permanent  masonry  lining  can  be  put  in  place.  As  timber  is 
perishable  in  any  but  very  wet  tunnels,  it  should  be  removed 
wherever  this  is  possible;  and  it  is  economy  to  use  the  timbers 
over  again  where  this  can  be  safely  done.  The  best  system 
of  timbering,  therefore,  is  one  that  permits  proper  drainage 
and  the  maximum  of  room  to  handle  the  material ;  that  is,  suf- 
ficiently strong  for  the  forces  to  be  contended  with,  and  that 
permits  ready  handling  of  the  separate  members  and  the  re-use 
of  the  bulk  of  the  timbers. 

For  timbering  purposes  a  soft,  elastic  evergreen  wood  is  gen- 
erally preferable  to  oak  or  other  hard  woods.  Pine  wood  is 
straight  of  grain,  lighter  and  easier  to  handle;  it  is  soft  enough 
to  cushion  a  sudden  thrust  in  bad  ground ;  and  as  it  will  bend 
before  breaking,  it  gives  warning  of  coming  danger. 

The  methods  of  tunnel  attack,  timbering,  sequence  of  lining, 
etc.,  as  generally  illustrated  in  Fig.  i8a,  vary  widely  in  different 
countries ;  and,  mainly  for  purposes  of  general  reference,  the 
essential  features  of  the  principal  methods  are  briefly  described. 

English  Method  as  Applied  in  the  United  States. — The  main 
features  of  this  system  of  tunneling  are  the  driving  of  a  top- 
heading  ;  the  widening  out  laterally  from  this-  heading  and  the 
excavation  of  the  full  section  of  the  arch ;  the  removal  of  the 
bench  immediately ;  and,  particularly,  the  use  of  heavy  crown- 
bars  of  timber  to  hold  up  the  roof  timbers,  and  the  withdrawal 
of  these  crown-bars  as  the  work  progresses,  whenever  this  can 
be  safely  clone. 

The  advantages  of  this  'system  are  summarized  by  its  ad- 
vocates as  follows :  The  large,  free  space  provided  facilitates 
drainage,  ventilation,  and  the  easy  and  economical  removal  of 
the  debris,  this  debris  being  either  taken  directly  from  the 


68 


MODERN   TUNNEL  PRACTICE 


bench,  or  run  into  cars  in  a  bottom  heading.  Where  the  crown- 
bars  can  be  withdrawn  and  re-used  there  is  a  saving  of  time, 
material  and  labor  in  bringing  down  new  sets.  As  the  crown- 
bars  are  drawn  after  the  arch  is  in  place,  this  system  does  not 
interfere  with  the  masons  as  tnuch  as  a  system  requiring  the 
timbers  to  be  removed  as  the  arch  is  built. 

The  objection  is  made  that  this  system  requires  the  miners 


FIG.  19. — English-American  Tunnel  System;  as  Applied  at  the  Musconet- 

cong  Tunnel. 

to  be  idle  while  the  masons  are  at  work;  but  the  work  can  be 
so  arranged  that  other  work  can  be  found  for  the  miners. 

The  English  system  has  been  successfully  used,  with  various 
modifications,  for  over  fifty  years  in  England,  in  America,  and 
on  the  Continent;  and  even  in  earth  and  comparatively  soft 
ground  it  can  be  safely  and  economically  applied.  The  two 
cases  (Figs.  19  and  iQa)  used  for  illustration  are  taken  from 
the  Musconetcong  and  the  Hoosac  tunnels. 


PRINCIPLES  OF  TUNNEL  TIMBERING  AND  DRIVING 


69 


Belgian  and  Belgian-German  System. — The  Belgian  engineers 
were  the  first  to  build  the  arch  first,  underpin  this  arch  and 
build  the  side  walls  last,  this  process  being  illustrated  in  Figs. 
20  and  21.  It  commences  with  a  top-heading,  which  is  en- 
larged laterally  until  it  includes  the  whole  arch  area.  The_ 
underpinning  of  the  completed  arch,  preparatory  to  building 


FIG.    iQa. — English- American  Tunnel    System;   as  Applied   at  the   Hoosac 

Tunnel. 

one  of  the  side  walls,  is  shown  in  the  illustration.  Both  illustra- 
tions are  taken  from  Mr.  Drinker's  description  of  the  St.  Cloud 
tunnel. 

In  the  German  modification  of  the  Belgian  system  the  cen- 
tral core  is  left  to  support  the  roof  timbering;  but  the  side 
drifts  are  excavated,  and  in  these  the  side  walls  are  built,  the 
arch  being  constructed  last.  French  engineers  have  also 
adopted  the  central  core  system  for  some  of  their  tunnels,  but 
they  build  the  arch  first,  as  in  the  original  Belgian  system. 


70 


MODERN    TUNNEL    PRACTICE 


The  claimed  advantage  of  the  Belgian  system  is  that  it  pro- 
vides a  speedy  and  secure  roof  under  which  to  carry  on  the 
rest  of  the  work  of  excavation  and  masonry.  But  this  con- 
tention is  only  true  when,  the  roof  is  a  loose  rock,  demanding 
some,  but  comparatively  little,  support. 

•The  disadvantages  are  many.     In  the  first  place  the  main 


FIG.  20. — The  Belgian  Tunnel  System :    St.  Cloud  Tunnel. 

cross-sectional  area  of  the  tunnel  is  not  at  once  accessible ;  and 
the  successive  removal  of  comparatively  small  sections  at  a 
time  is  very  uneconomical.  The  underpinning  of  the  arch  is 
also  very  objectionable  to  English  and  American  engineers; 
though  Continental  engineers  have  done  some  good  work  in  this 
direction,  notably  in  the  St.  Gothard  tunnel.  In  this  Belgian 
system  the  handling  of  the  material  and  removal  of  the  debris 
are  difficult  and  costly  in  the  small  openings  provided; 
and  this  is  especially  true  in  building  the  arch  and  the  side 


PRINCIPLES  OF  TUNNEL  TIMBERING  AND  DRIVING  JI 

walls.  The  tunnel  is  also  drained  at  a  disadvantage,  as  a  bot- 
tom heading  driven  for  this  purpose  tends  to  loosen  the  sides 
and  weaken  the  temporary  supports  of  the  completed  arch. 
And  under  a  common  arrangement  of  the  timbering  support- 
ing the  arch  there  is  a  decided  tendency  to  concentrate  the  load 
on  a  single  part  of  the  central  core.  This  is  contrary  to  all 
good  tunnel  practice. 

German  System. — While  modified  in  a  number  of  ways,  and  as 
conditions  may  dictate,  the  essential  feature  of  this  system,  as 


FIG.  21. — Belgian  System;  Showing  Centers  and  Method  of  Underpinning 

the  Arch. 

shown  in  Figs.  22  and  22a,  is  a  central  core  used  for  support- 
ing the  roof.  A  top-heading  is  usually  driven  first,  and  this 
is  gradually  widened  laterally  until  it  includes  the  entire  arch 
section.  The  excavation  for  the  side  walls  is  then  made  from 
the  top  down,  and  the  building  o>f  the  side  walls  precedes  arch 
construction.  In  some  cases,  however,  the  side  walls  are  started 
in  two  bottom  drifts,  which  meet  the  top-heading  enlargement. 
The  German  engineers  claim  that  this  central  core  provides 


72  MODERN    TUNNEL    PRACTICE 

cheap  working  in  hard  ground ;  and  as  the  system  is  based  upon 
relatively  small  openings,  in  soft  ground  the  pressures  can  be 
better  met.  The  use  of  the  core  is  also  supposed  to  save  much 
timbering. 

But  even  in  Germany  the  system  is  now  practically  aban- 
doned because  of  its  defects.  Owing  to  these  small  openings 
the  work  is  inconvenient  and  costly;  the  ventilation  is  bad; 
bad  bonding  is  apt  to  result  from  the  cramped  space  in  which 


FIG.  22. — German  System:  Triebitz  Tunnel. 


the  masonry  of  the  side  walls  has  to  be  laid ;  it  is  very  difficult 
to  preserve  the  alignment  in  a  tunnel  so  constructed,  and  the 
arrangement  of  the  timbering  tends  to  a  dangerous  concentra- 
tion of  load  and  pressure. 

Austrian  System. — In  its  final  development  this  system  is  char- 
acterized by  a  very  strong  timber  support  during  exploitation. 


PRINCIPLES  OF  TUNNEL  TIMBERING  AND  DRIVING 


73 


It  commences  with  a  central  bottom-heading-;  immediately 
above  this  is  driven,  a  second  heading  extending  to  the  top  of 
the  arch  masonry;  this  last  heading  is  enlarged  laterally  until 
it  takes  in  the  whole  arch  area ;  and  finally  the  bottom- heading 
is  enlarged  laterally  until  it  includes  the  side-wall  area.  - 
side  walls  are  built  first,  and  the  arch  is  then  made. 

The  completed  timbering  arrangement  is  here  shown  from 


FIG.  22a. — German  System:    Ozernitz  Tunnel. 

illustrations  taken  from  Drinker's  "Tunneling."  The  Aus- 
trian engineer,  Rziha,  advocates  this  system  for  all  kinds  of 
ground,  from  loose  rock  to  quicksands. 

In  this  Austrian  system  the  central  bottom-heading  is  a  good 
feature,  as  it  well  provides  for  ventilation  and  drainage.  The 
general  arrangement  of  the  supporting  timbers,  though  some- 
times crowded,  is  effective  as  a  rule.  All  cross  and  longitudinal 


74 


MODERN    TUNNEL    PRACTICE 


connections  are  well  designed ;  there  is  no  undue  concentration 
of  load  at  any  one  point,  and  the  space  left  for  the  removal 
of  the  debris  and  the  work  of  the  masons  is  ample,  as  compared 
with  the  preceding  systems. 

The  one  marked  disadvantage  of  the  system  is  the  over- 
crowding of  the  timbers,  requiring  a  large  amount  of  material 
and  handling,  and  to  that  extent  decreasing  the  room  available 
for  work. 

American  System. — The  so-called  American  system,  as  shown 


FIG.  23.— Austrian  System;  Advance  Heading  and  Top  Enlargement. 

in  Fig.  24,  is  a  development,  and  it  had  its  origin  in  the  condi- 
tions imposed  by  the  character  of  the  rock  through  which  a 
number  of  the  earlier  American  tunnels  were  driven.  These 
tunnels  were  largely  located  in  the  coal  regions,  in  slates,  shales, 
and  other  weak  rock  requiring  ample  support.  The  system  it- 


PRINCIPLES  OF  TUNNEL  TIMBERING  AND  DRIVING 


75 


self  more  nearly  resembles  the  Austrian  method  than  it  does 
others  described ;  but  it  is  much  more  economical  of  timber. 

In  this  manner  of  driving  a  tunnel  a  central  top-heading  is 
usually  first  driven,  and  this  is  enlarged  sideways  so  as  to  in- 
clude the  full  arch  area.  The  bottom  is'  taken  out  m  4wa 
benches  as  the  work  progresses. 

But  the  essential  feature  of  the  system  is  the  construction 
of  the  roof  support.  This  is  made  of  nine  or  more  arch  blocks, 


FIG.    233. — Austrian    System;    Arch    Area    Enlargement. 

or  wooden  voussoirs,  well  jointed  and  connected,  carried  upon 
longitudinal  wall  plates  resting  upon  posts,  the  latter  either 
with  or  without  a  sill. 

In  the  earlier,  and  in  some  of  the  later  Western  American 
tunnels,  this  timber  lining  was  lagged  and  left  in  place,  well 
packed  outside  with  broken  stone.  This  was  simply  a  measure 
of  original  economy  of  construction,  as  the  rotting  of  the  tim- 


76 


MODERN    TUNNEL    PRACTICE 


bers  and  the  danger  from  fire  sooner  or  later  demanded  a 
more  permanent  lining  of  brick,  stone  or  concrete. 

A  simple  application  of  the  American  system  of  timbering 
is  here  shown  in  an  illustration  of  the  Little  Tom  tunnel,  on 
the  Norfolk  &  Western  Railway,  built  in  1888-90.  The  ma- 
terial penetrated  was  a  gray  sandstone,  in  approximately  hori- 
zontal beds,  and  cut  at  times  by  the  coal  seams  of  that  section. 
These  rock  beds  varied  in  thickness  from  a  few  inches  to  sev- 


FIG.    23b. — Austrian  System ;  Section  Completely  Excavated. 

eral  feet;  and  the  rock  itself  disintegrated  upon  exposure  to 
the  air,  and  thus  required  ample  timbering. 

The  dimensions,  location  and  form  of  the  timbers  are  shown 
in  Fig.  24.  The  wood  used  was  first-class  white-oak,  and 
originally  it  was  left  in  the  tunnel  as  a  protection  against  fall- 
ing rock  during  the  early  operation  of  the  road.  Where  the 
rock  was  comparatively  sound  the  three  roof-segments  were 
alone  used,  supported  in  "niches"  cut  in  the  rock;  but  as  a  rule 


PRINCIPLES  OF  TUNNEL  TIMBERING  AND  DRIVING 


77 


the  3-inch  lagging  shown  was  laid  on  these  segments,  forming 
a  continuous  protection. 

In  a  letter  to  Engineering  News*  Mr.  Emile  Lowe,  C.E., 
gives  the  cost  of  this  work  as  follows:  The  amount  of  timber-- 
ing per  lineal  foot  approximated  250  feet  board  measure,  _A 
part  of  this  timbering  was  done  by  day  labor,  and  the  remainder 
under  a  contract  of  $60  per  thousand  feet  board  measure.  The 
timbering  actually  cost  about  $15  per  lineal  foot.  The  area  of 
the  rock  section  was  263.66  square  feet,  equivalent  to  9.765 
cubic  yards  per  lineal  foot.  The  area  of  the  timbered  section 


Cross  Section.  Longitudinal  Section. 

FIG.    24. — American    Tunnel    System:      Little    Tom    Tunnel,    Norfolk    & 
Western  Railroad. 

of  the  tunnel  was  314.16  square  feet,  or  11.635  cubic  yards 
per  lineal  foot.  The  contract  price  for  excavation  was  $3.50 
per  cubic  yard ;  so  that  the  respective  costs  of  the  two  sections 
for  excavation  were  $34.17  and  $40.72  per  lineal  foot.  Some 
allowance  was  made  for  breakage  outside  of  the  theoretical  sec- 
tion of  the  tunnel,  and  for  this  outside  work  the  contractor 
was  allowed  $1.50  per  cubic  yard.  Stone  packing  over  the 
timbers  was  paid  for  at  the  rate  of  $1.50.  The  total  cost  of 
the  tunnel  was  thus  about  $115,000,  divided  about  as  follows 
in  relative  cost : 

Excavation,  per  lineal  foot $43.00 

Timbering,  per  lineal  foot 16.00 

Packing,  per  lineal  foot i.oo 


Total  cost  per  lineal  foot 

^Engineering  News,  April  19,  1900. 


$60.00 


7«  MODERN    TUNNEL    PRACTICE 

This  tunnel  was  driven  partly  by  hand  and  partly  by  ma- 
chine drills;  and  the  daily  progress  ranged  from  2  feet  to  6 
feet  in  the  heading,  and  from  2  feet  to  4  feet  in  the  bench. 

Driving  Through  Loose  Gravel. — A  good  example  of  the 
American  method  of  driving  a  tunnel  through  loose  gravel  is 
here  taken  from  an  article  on  the  tunnel  on  the  Crow's  Nest 
Pass  line,  Canadian  Pacific  Railway,  written  by  C.  R.  Coutlee, 
C.E.,  of  Vancouver,  B.  C.* 

This  tunnel  was  only  900  feet  long,  but  it  passed  through  a 
loose  and  comparatively  dry  gravel  for  its  entire  length.  The 


Chute 
Cross  Brace 

Car-^L 


\Cribhing  of  2" Planks  •'•  ':"•' 
EX-       for  Post  Chambers 


Longitudinal      Section. 


5      VL     ti    «ff 
Diagram  Plan. 

FIG.  25. — Crow's  Nest  Pass  Tunnel ;  Longitudinal  Section  and  Plan.  Show- 
ing Method  of  Driving. 

method  adopted  for  driving  was  practically  as  follows,  the  di- 
mensions of  the  tunnel  being  indicated  on  the  accompanying 
illustration  (Fig.  26)  : 

In  the  arch  area  of  the  tunnel  two  side  drifts,  8  feet  high 
and  6  feet  wide,  were  driven,  leaving  about  8  feet  of  material 
between  them.  The  frames  of  these  drifts  were  made  of  8-inch 
round  mountain  fir.  A  sill-piece  6  feet  long^  was  first  set  accu- 
rately to  the  elevation  of  the  under  side  of  the  wall  plate;  on 
^Engineering  News,  April  2,  1903. 


PRINCIPLES  OF   TUNNEL   TIMBERING  AND  DRIVING. 


79 


this  were  set  up  the  posts ;  and  the  cap,  4  feet  long,  was  flatted 
and  gained  down  i  inch  upon  the  posts  to  form  a  small  shoulder 
and  prevent  squeezing  in. 

With  the  drift-frame  in  place  the  face  in  front  was  walled 
with  i -inch  breast-boards,  braced  with  inclined  struts.  ^All 
around  the  outside  of  the  frame  close  lagging  was  entered  and 
driven  forward  by  sledges.  This  lagging  was  made  of  2x4- 
inch  mountain  fir,  in  5-foot  lengths.  Each  piece  was  first 
driven  about  half  way,  with  an  upward  and  outward  lead,  mak- 
ing as  close  joints  with  its  neighbor  as  possible.  With  a  2-foot 
hood  thus  secured,  the  miner  carefully  removed  the  top  breast- 


FIG.    26. — Transverse    Section ;    Showing   Method   of   Excavating   and 

Timbering. 

board,  and  was  met  with  a  flow  of  gravel.  But  he  stopped 
this  flow  by  pushing  the  board  ahead  about  2  feet  and  wedging 
it  in  place.  The  next  board  was  removed  and  pushed  forward 
in  like  manner,  and  the  operation  was  repeated  until  the  whole 
breast  of  the  drift  had  been  advanced  about  2  feet. 

As  the  advanced  lagging  was  subjected  to  side  and  top  pres- 
sures, and  only  held  by  the  precarious  support  given  by  the 
breast-boards  advanced,  to  secure  a  better  support  a  false  frame 
of  lighter  timber  was  now7  set  up.  With  the  latter  in  place 
the  lagging  was  driven  forward  its  full  length,  and  the  breast- 


8O  MODERN    TUNNEL    PRACTICE 

boards  were  separately  advanced  as  before ;  and  finally  a  second 
true  frame  was  erected  about  4  feet  from  the  first  one. 

The  almost  fluid  pressure  of  the  gravel  was  too  great  to 
allow  the  insertion  of  a  new  set  of  lagging  to  wedge  out  the 
lagging  already  in  place.  But  the  upward  and  outward  flare 
given  the  lagging  brought  the  points  about  4  inches  outside  the 
second  frame.  This  space,  outside  the  posts  and  cap,  was 
bridged  by  2-inch  scantling,  blocked  off  from  the  frame  by 
2-inch  blocks ;  and  beneath  this  bridge  the  new  lengths  of  lag- 
ging were  driven.  As  it  was,  considerable  friction  was  en- 
countered. 

After  the  side  drifts  had  advanced  about  20  feet,  the  top- 
heading  was  driven  in  a  similar  manner,  though  this  was 
only  4  feet  high,  and  the  8-foot  cap  required  a  middle  prop. 
This  top-heading  connected  the  side  drifts  at  the  top ;  the  top 
lagging  of  the  side  galleries  was  broken  through,  and  the  block 
arch  of  five  12  x  1 2-inch  timbers  was  set  up  on  the  wall  plates, 
the  latter  being  also  12  x  1 2-inch  sticks,  shaped  on  top  to  fit  a 
"crow- foot"  or  V-shaped  notch  on  the  arch  timber,  and  bored 
at  15-inch  intervals  for  dowels.  At  each  joint  of  the  arch 
f-inch  round  iron  dowels,  6  inches  long,  were  inserted.  In 
this  tunnel  the  arch  sets  and  vertical  posts  were  placed  only 
3  inches  apart. 

As  the  lower  bench  was  excavated  the  two  sides  were  breast- 
boarded  with  2-inch  plank ;  but  the  central  part  was  allowed  to 
assume  a  slope.  Round,  6-inch  timbers  were  placed  hori- 
zontally, as  the  digging  progressed,  across  the  tunnel  at  the 
level  of  the  wall  plates  and  at  5-foot  intervals ;  and  another  tier 
of  the  same  bracing  was  located  7  feet  lower  down.  Against 
these  struts  the  lower  boarding  was  braced. 

In  excavating  the  post-chambers  the  top  breast-board  was  re- 
moved and  the  gravel  scraped  away  sufficiently  to  allow  this 
board  to  be  set  forward  3  feet.  A  side-board  was  then  in- 
serted parallel  to  and  just  outside  the  wall  plate  to  prevent  side- 
runs.  In  this  manner  a  chamber  was  cribbed  down  to  grade 
at  each  side;  and  at  grade  a  12  x  1 2-inch  sill  2  feet  long  was 
set.  A  post  was  then  entered  under  the  wall  plate  and  resting 


PRINCIPLES  OF  TUNNEL  TIMBERING  AND  DRIVING 


8l 


on  the  sill,  and  the  bottom  of  the  post  was  pushed  outward  by 
a  jack  until  the  post  was  plumb.  Great  force  was  required  to 
do  this,  but  a  tight  fit  .was  secured. 

While  excavating  the  post-chambers  the  unsupported  wall 
plate  formed  a  bridge,  about  3  feet  long,  from  the  gravel  of 
the  bench  to  the  posts  already  in;  the  drift-frames  assisted  in 
holding  up  these  plates.  When  the  ground  would  permit  it,  a 
space  for  two  posts  was  excavated  at  one  time. 

At  this  tunnel  an  advance  of  about  21  feet  per  week  was 
made,  and  the  cost  amounted  to  about  $77  per  lineal  foot  for 
labor,  timber  and  supplies.  The  timber  lining  was  left  in  the 
tunnel  permanently. 

Crutch  System. — The  Lake  View  tunnel,  under  Lake  Michi- 


In  Good  Ground. 


.  -     .  ,  ,  .  .  ... 
in  weroanaand  Loam. 


FIG.  27.—  The  Crutch   System  of  Tunnel  Driving. 

gan  at  Chicago,  111.,  is  two  and  two-thirds  miles  long,  and  it 
was  driven  through  different  grades  of  clay,  with  occasional 
pockets  of  sand.  The  standard  section  was  circular,  8  feet  and 
10  feet  in  diameter  inside. 

Owing  to  excessive  excavation  resulting  from  methods  pre- 
viously followed,  Mr.  Paul  G.  Brown,  engineer  in  charge, 
adopted  the  so-called  crutch  and  crown-bar  system  of  timber- 
ing, here  shown  in  Fig.  27. 

In  this  system  horizontal  wall  plates  were  first  let  into  the 
sides  of  the  excavation  about  on  the  line  of  the  horizontal  diam- 
eter. Upon  these  plates  rested  pairs  of  6  x  8-inch  timbers,  form- 


82 


MODERN    TUNNEL    PRACTICE 


ing  inverted  V's,  with  the  apex  supporting  a  longitudinal  tim- 
,ber.  Upon  the  outside  of  the  V's,  or  crutches,  blocking  was 
placed  to  hold  other  longitudinals  supporting  the  sides.  The 
number  of  these  latter  timbers  varied  with  the  character  of  the 
soil. 

A  6  x  8-inch  sill  was  placed  at  the  face,  and  the  face  was 
bulkheaded  to  form  a  bearing  for  the  sill.     One  set  of  crutches 


tross '^SectilorC"  Longitudi 

FIG.  28. — Tunneling  Through   Sand:   Brooklyn,   N.  Y. 

was  used  to  support  the  bars,  midway  between  the  face  and  the 
finished  masonry,  the  rear  end  of  the  bars  being  carried  by  the 
masonry,  and  the  front  end  by  posts  at  the  face.  All  of  the 
timbers  were  set  up  by  wedges.  The  progress  made  was  about 
14  feet  per  day;  costing  $24.41  per  lineal  foot  in  clay,  and 
$38  in  rock. 

Timbering  a  Sand  Tunnel. — The  timbering  here  described  was 
used  in  building  a  circular  sewer,  13  feet  6  inches  clear  diam- 
eter, in  Brooklyn,  N.  Y. ;  the  work  was  designed  by,  and  was 
executed  under,  the  direction  of  Henry  R.  Asserson,  Chief  En- 
gineer of  Sewers.  This  sewer  tunnel  was  lined  with  16  inches 
of  brickwork,  with  a  granite  block  invert.  The  "tunnel  was 
driven  through  fine  sand  carrying  considerable  water.  This 
sand  would  not  stand  up  during  excavation,  but  was  hardly 


PRINCIPLES  OF  TUNNEL  TIMBERING  AND  DRIVING  83 

unstable  enough  to  be  classed  as  quicksand.    The  work  was  car- 
ried on  from  two  shafts. 

In  excavating  this  tunnel  (Fig.  28)  a  drift  6  feet  wide  and 
7  feet  high  was  first  driven  at  the  bottom  center  of  the  sec- 
tion. The  primary  purpose  of  this  drift  was  to  drain  the  sand, 
and  to  facilitate  this  a  tile  sub-drain  was  laid  about  2  feet  be- 


FIG.  29. — Meem  Peking-board  System. 

low  the  bottom  of  the  invert  and  left  in  place.  Almost  simul- 
taneously with  the  bottom  drift,  another  drift  was  driven  at  the 
top  of  the  section,  8  feet  wide  and  7  feet  high ;  and  both  drifts 
were  kept  about  50  feet  ahead  of  the  full  section  work.  As 
they  were  driven,  these  drifts  were  held  by  the  usual  frame  and 


FIG.  30. — Detail  of  Meem  Poling-board. 

poling-boards,  with  the  face  bulkheaded  and  held  up  by  struts, 
or  rakers. 

The  section,  was  enlarged  from  the  heading  by  excavating 
on  each  side,  inserting  the  roof-bars,  radial  struts  and  poling- 
boards  one  after  the  other,  as  shown  in  the  illustration.  The 
radial  struts  were  removed  as  the  lining  was  built ;  but  all  other 
timbering  was  left  in  place,  with  all  the  interstices  rilled  with 
concrete. 


84 


MODERN    TUNNEL    PRACTICE 


Meem  Poling-board  Method. — For  another  sewer  tunnel  in 
Brooklyn,  driven,  through  the  same  water-bearing  fine  sand, 
Mr.  J.  C.  Meem,  C.E.,  devised  the  plan  here  shown  in  Fig.  29. 

In  this  method  a  top-heading  was  first  taken  out,  embracing 
about  one-quarter  of  the  perimeter  of  a  circular  section  17  feet 
8  inches  diameter.  The  segment  guide- frame  A  B  C  D  E 
was  then  erected,  and  over  the  top  of  this  was  slipped  the 
ends  of  five  special  iron  poling-boards  (Fig.  30) .  These  boards 
were  gradually  pushed  forward  as  the  excavation  progressed 
beneath  them,  and  other  guide-frames  were  successively  set 
up,  until  there  were  five  of  these  frames  under  the  boards. 

To  next  carry  down  the  excavation  on  each  side  the  roof 
was  temporarily  braced  by  the  struts  E  F  G  supporting  lag- 
ging. As  soon  as  the  side  cuts  were  completed  the  segmental 


FIG.  31. — Iron  Crown-bar  System  of  Tunneling. 

frame  H  I J  K  was  set  up,  and  struts  were  inserted  to  relieve 
the  poling-boards  and  temporary  timbering.  The  excavation 
was  carried  on  down  the  sides  by  lagging  and  radial  struts, 
until  the  section  had  been  sufficiently  opened  to  permit  the 
building  of  a  portion  of  the  invert.  The  timber  frame  L  M  N  O 
was  then  built,  and  the  weight  of  the  segmental  timbering 
was  transferred  to  the  invert.  The  excavation  was  now  ready 
for  the  completion  of  the  lining  masonry.  To  build  this 
masonry  segmental  centers  were  used,  with  the  frames  erected 


PRINCIPLES  OF  TUNNEL  TIMBERING  AND  DRIVING  85 

between  the  timbering  sets,  the  latter  being  removed  as  the 
masonry  progressed. 

As  shown  in  the  cut,  the  poling-boards  used  at  the  top  have 
steel-shod  cutting  edges  and  a  steel-plate  tail-piece  with  small 
I-beam  stiffeners  beneath.  In  operation  the  tail-piece  over- 
lapped the  roof-lagging.  The  poling-boards  were  driven  ahead 
by  30  and  6o-ton  hydraulic  jacks,  operated  by  a  hand  pump. 
The  face  of  the  heading  was  generally  kept  about  30  feet  ahead 
of  the  brickwork. 

Iron  Crown-bar  System. — The  King's  Cross  Station  tunnel, 
driven  in  1890  in  London,  England,  is  only  1,590  feet  long, 


FIG.  3ia. — Needles  Used  in  Iron  Crown-bar  System. 

but  it  passes  under  the  Regent's  Canal,  with  only  6  feet  of  earth 
above  the  tunnel  at  some  places.  The  tunnel  is  generally  circu- 
lar, with  a  clear  diameter  of  26  feet,  and  is  lined  with  brick 
throughout. 

In  this  case — and  especially  to  reduce  the  head  room  required 
by  timber — the  ordinary  timber  crown-bars  were  replaced  by  a 
series  of  iron  and  steel  "needles,"  grooved  longitudinally  so 
that  the  bars  link  together  and  yet  have  sufficient  play  to  allow 
them  to  take  the  form  of  the  arch.  As  it  was  difficult  to  roll 
the  double-needle,  two  ordinary  needles  were  joined  by  counter- 
sunk rivets,  as  shown  in  Fig.  31  a. 

The  needles  here  used  are  10  feet  long,  6  inches  wide  and 
2  inches  deep.  As  soon  as  the  brickwork  is  built  under 
their  protection,  the  needles  are  pushed  forward  in  sets  of 


86 


MODERN    TUNNEL    PRACTICE 


three,  until  only  one  or  two  feet  of  the  needles  rest  upon  the 
brickwork;  and  as  the  needles  are  pushed  forward  by  screw- 
jacks,  they  are  held  up  by  successive  segmental  frames  of 
the  ordinary  type.  To  facilitate  the  forward  motion  of  the 
needles,  holes  are  drilled  at  intervals  along  each  needle;  into 
these  holes  the  two  bosses  of  a  bracket  are  set,  and  against  this 
bracket  the  screw-jack  pushes. 

Crown-bars  of  Old  Rails. — The  Marsden  tunnel  on  the  Lon- 
don &  Northwestern  Railway,  in  England,  was  driven,  in 
1893,  by  tne  English  method  of  timbering.  Wooden  crown- 
bars  were  used  in  part  of  the  tunnel;  but,  to  decrease 
the  amount  of  excavation  and  packing,  Mr.  A.  A.  Macgregor, 
Resident  Engineer,  suggested  the  method  described  in  Fig.  32. 


E  NO.  NEW: 

FIG.  32. — Crown-bar  of  Old  Rails. 

To  each  side  of  a  3  x5^-inch  timber  he  through-bolted  two 
75-pound  bullhead  steel  rails,  worn  out  in  service.  The  crown- 
bars  thus  made  were  cheaper  than  the  all-timber  bars,  saved 
one-half  or  more  in  excavation  and  packing  and  were  easier  to 
handle.  Tests  made  showed  that  this  crown-bar  was  equal  in 
strength  to  a  round  larch  bar  1 1  inches  in  diameter,  under 
similar  conditions  of  loading. 

The  chief  objection  to  the  rail-bars  is  their  stiffness.  Their 
maximum  deflection  is  about  one-half  that  of  the  larch  bars; 
and  they  are  somewhat  treacherous  and  have  to  be  carefully 
watched  against  undue  stress.  They  do  not  give  warning  by 
bending  to  the  same  extent  as  the  all-wood  bar. 

Steel-lined  Tunnel — While  not  properly  coming  under  the 
head  of  tunnel  timbering  or  driving,  the  tunnel  here  described 


PRINCIPLES  OF  TUNNEL  TIMBERING  AND  DRIVING  / 

is  sufficiently  curious  to  be  noted.  In  the  Cripple  Creek  mining" 
region  it  was  necessary  to  extend  the  line  of  the  Golden  Circle 
Railway  through  the  dumping  ground  of  the  Portland  mine; 
and  to  meet  the  conditions  a  steel  covered  way  was  constructed 
which  would  be  gradually  converted  into  a  tunnel  by  the  opesa-- 
tion  of  dumping  the  waste  from  the  mine. 

This  way  was  242  feet  long,  14  feet  wide  inside,  10  feet  high 
to  the  springing  line,  and  was  roofed  with  a  semicircular  arch 
of  7-foot  radius.  It  was  made  of  steel  posts  and  arches  resting 
on  soft  cast-iron  piles.  These  piles  were  hollow,  12  inches  in 
diameter  outside  and  i  inch  thick;  they  averaged  8  feet  in 
length  and  were  spaced  8  feet  between  centers.  The  point  of 
the  pile  was  solid  for  half  its  length  and  a  timber  core  was  used 
in  driving  them.  After  the  tops  had  been  cut  to  a  level  by  pipe- 
cutting  machines,  a  cast-iron  cap  was  put  on  each  pile ;  and  on 
these  caps,  on  lead  plates,  were  laid  two  sets  of  12-inch  31- 
pound  longitudinal  I-beams.  The  calculated  load  on  each  pile 
was  56  tons ;  and  the  pile  foundation  cost  $7  per  lineal  foot  of 
tunnel. 

Each  post  was  made  of  two  1 2-inch  31 -pound  I-beams,  hav- 
ing a  bearing  surface  of  12  x  14  inches  on  each  pile;  the  posts 
being  spaced  2  feet  apart,  center  to  center.  Attempts  were  first 
made  to  bend  the  tops  of  the  posts  so  as  to  form  a  half  arch. 
But  this  failed,  and  each  half  arch  was  made  of  web  and  angles 
in  three  4- foot  sections,  spliced  with  f-inch  plates;  a  ^-inch 
plate  was  used  for  a  connection  with  the  posts. 

For  lateral  bracing  an  8-inch  I-beam  crosses  under  the  track 
and  connects  the  longitudinals  at  each  set  of  piles.  At  the  top 
of  the  arch  another  8-inch  longitudinal  ties  each  arch  to  its 
neighbor,  and  8-inch  channel  irons  connect  the  sets  at  the 
springing-lines  on  each  side  and  outside  the  posts.  The  roof 
covering  and  siding  is  made  of  3-inch  red  spruce  timber;  but 
as  this  rots  away  it  will  be  replaced  with  two  rings  of  brick. 

The  cost  of  the  steel  work  and  planking  amounted  to  about 
$50  per  lineal  foot  of  tunnel,  in  1898. 

Sand-chamber  and  Caisson  Method.* — The  Meudon  tunnel,  on 

^Engineering  News,  Sept.   n,  1902. 


88 


MODERN    TUNNEL    PRACTICE 


the  new  line  between  Paris  and  Versailles,  was  completed  in 
1902,  after  encountering  difficulties  which  were  surmounted  in 
the  following  manner : 

The  tunnel  penetrates  a  marl  formation  overlaid  by  water- 
bearing sands.     Work  was  commenced  with  a  Clichy-type  of 


Fkj.3. 


FIG.  33.  —  Meudon  Tunnel  :  Sections  Showing  Temporary  Interior  Walls, 
and  the  Transverse  Gallery  at  the  Point  of  Commencing  Attack  on 
the  Debri's  near  the  Top  of  the  Tunnel. 

shield;  but  this  was  soon  deformed  and  heavy  and  careful  tim- 
bering was  resorted  to.  At  one  point  the  marl  very  closely 
approached  the  sand  ;  the  marl  swelled  on  exposure  to  the  air, 
and  water  finally  broke  through  from  above,  and  a  serious 
cave-in  occurred  when  only  115  feet  of  the  side  walls  remained 


Oev«rion. 


S  ectional     Pla  n . 


FIG.  33a. — Meudon  Tunnel :  Detail  Showing  the  Construction  of  a  "Sand- 
chamber." 

to  be  built.     The  difficult  work  lay  in  tunneling  through  this 
mass  of  marl,  sand,  water  and  broken  masonry. 

The  first  operation  was  to  build  strong  masonry  bulkheads 
across  the  tunnel  to  confine  the  cave-in,  leaving  small  passages 
through  these  bulkheads  that  could  be  quickly  closed.  Then  a 


PRINCIPLES  OF  TUNNEL  TIMBERING  AND  DRIVING 


89 


small  gallery  was  driven  outside  the  masonry  standing,  with 
the  view  of  draining  the  cave  down  grade  toward  Paris. 

Two  temporary  walls  were  then  built  inside  and  parallel  to 
the  axis  of  the  tunnel  to  better  support  the  arch-centers,  and 
this  was  done  in  ordinary  drifts  and  without  great  trouble. 
(See  Fig.  33).  The  Versailles  end  of  the  cave  was  soon 
reached ;  and  as  the  central  part  of  the  mass  was  relatively  free 
from  quicksand,  a  cross-heading  was  driven  through  it  and 


Fourth 

Stage. 


FIG.  34. — The  Four  Successive  Stages  of  Emptying1  a  Sand-chamber: 
a  =  roof  of  pieces  13x13  cm.,  raking  and  jointed  ;  b  =  transverse  poling- 
boards  13x13  cm.,  with  a  jog;  c  =  horizontal  pieces  6x18  cm.;  d  =  ad- 
vance poling  in  pieces  20x25  cm. 

centers  were  erected  upon  the  temporary  longitudinal  and  the 
side  walls  for  building  the  arch.  But  the  building  of  this  arch 
proved  to  be  a  long,  difficult  and  costly  operation.  The  fine 
sand,  carrying  water,  was  almost  fluid ;  the  use  of  compressed 
air  was  impossible  owing  to  the  enormous  water  pressure,  and 
the  freezing  process  could  not  be  resorted  to,  owing  to  the  im- 
possibility of  driving  pipes  horizontally  through  the  broken 
arch  masonry  imbedded  in  the  sand. 


9o 


MODERN    TUNNEL    PRACTICE 


In  this  emergency  the  engineers  devised  the  "sand-chamber" 
method  (Fig.  34).  The  advance  was  made  in  a  concave  form 
and  maintained  by  a  system  of  small  boxes  formed  with  poling- 
boards,  completely  stopping  off  the  face.  This  was  done  by 
forcing  forward,  for  sides  and  roof,  a  series  of  6  x  6-inch 
squared  sticks,  as  closely  jointed  as  possible  and  sometimes 
caulked.  The  size  of  these  chambers  never  exceeded  one  cubic 
metre  in  volume,  and  in  each  the  face  was  bulkheaded.  The 
6  x  6-inch  timbers  were  forced  through  this  bulkhead  by  3<>ton 
hydraulic  jacks,  by  first  boring  holes  around  a  place  6  inches 
square  and  then  forcing  the  enclosed  block  ahead  of  the  timber. 
To  decrease  the  hydraulic  pressure  encountered,  the  timbers 
were  sometimes  bored  on  their  axis,  thus  permitting  the  sand 
and  water  to  flow  through  the  sticks  as  these  advanced.  Fin- 
ally the  pressure  became  so  great  that  beams  (Fig.  35)  6x6 


Interior  Caisson. 


1 
Section  C-D. 

FIG.  35. — Detail  of  Metal  Beams,  or  "Caissons,"  at  Versailles  End. 

inches,  outside,  were  made  with  two  channel  bars  and  two 
plates.  These  iron  beams  were  open  at  the  forward  end  and 
closed  at  the  rear,  with  an  opening  in  the  plugged  end  that  could 
be  closed  if  necessary. 

After  each  main  chamber  had  been  divided  by  the  above  de- 
scribed means  into  four  secondary  chambers  of  not  more  than 
one  cubic  yard  capacity,  each  new  chamber  had  to  be  emptied 
of  sand  and  the  bulkhead  pushed  forward.  This  was  very 
slow  and  dangerous  work,  and  it  is  only  necessary  to  say  that  to 
empty  one  chamber,  or  to  take  out  a  little  over  one  cubic  yard 
of  sand,  required  one  week's  time. 

When  the  arch  work  thus  constructed  approached  within  6J 
feet  of  the  crushed  end  of  the  standing  arch,  a  metallic  roof  was 
pushed  forward  from  the  top  of  the  advance  gallery  to  the  top 
of  the  arch  still  in  place.  This  roof  was  of  so-called  iron 


PRINCIPLES  OF  TUNNEL  TIMBERING  AND  DRIVING  QI 

"caissons/'  6  inches  square  and  10  feet  long,  pushed  forward 
by  7O-ton  rams  (Fig.  36). 

Though  the  new  arch  throughout  the  renewal  was  5.24  feet 
thick,  water  filtered  through  it  owing  to  the  enormous  pressure. 
To  stop  this  a  waterproof  tunnel  lining  was  put  in.  A  steel_ 
sheet  lining  imm.  thick,  was  made  into  a  ring  im.  wide  by 
soldering  the  joints,  and  these  rings  were  also  soldered  to- 
gether. This  sheet  lining  was  secured  to  oak  pegs  driven  in 
holes  drilled  in  the  masonry,  and  a  space  of  about  i^  inches  was 
left  between  the  lining  on  the  masonry,  which  was  filled  by 
injecting  cement  mortar.  To  hold  this  steel  shell  against  the 
outside  pressure  a  concrete  steel  lining  was  put  inside  of  it  and 
secured  to  bolts  passing  through  the  steel  shell  to  the  masonry 
This  concrete  steel  lining  was  about  13  inches  thick  at  the 


Cross  Section  A-B.  Longitudinal  Section. 

FIG.    36. — Method  of  Using  "Caissons,"  at  Versailles  End. 

crown,  9  inches  at  the  spring  and  1 1  inches  thick  at  the  base, 
and  imbedded  in  the  concrete  was  a  network  of  round  longitudi- 
nal, transverse  and  diagonal  rods,  of  varying  diameters. 

Pilot-tunnel  System — This  system  was  first  devised  and  used 
at  the  old  Hudson  River  tunnel  by  Mr.  John  Anderson,  general 
manager  for  the  contractor.  It  was  later  successfully  employed 
by  the  contracting  firm  of  Anderson  &  Barr  in  building  a  sec- 
tion of  the  Brooklyn  relief  sewer,  10  to  15  feet  diameter,  run- 
ning through  fine  sand  and  loose,  dry  gravel. 

The  pilot-system  is  especially  devised  for  tunneling  through 
soft  and  uncertain  material,  the  pilot  itself  furnishing  a  sup- 
port for  holding  the  roof,  as  well  as  the  centering  for  masonry. 

The  "pilot"  is  a  cylinder,  usually  6  feet  in  diameter,  made  up. 


92  MODERN    TUNNEL    PRACTICE 

of  curved  plates  of  boiler  iron  riveted  on  the  four  sides  to  light 
angle-irons  pierced  with  holes  for  bolts.  The  pilot  is  located  on 
the  axis  of  the  tunnel  (See  Fig.  37)  and  the  segments  are  bolted 
up,  commencing  with  the  roof -plates,  as  the  excavation  is  made 
from  within  the  pilot,  which  is  thus  pushed  forward  and  kept 
about  30  feet  in  advance  of  the  completed  section.  The  rear 
end  of  the  pilot  is  supported  by  timbering,  and  the  cylinder 
itself  acts  as  a  truss  over  the  short  invert  space. 

In  operation  the  material  is  carefully  removed  from  about 


FIG.  37. — The  Anderson   Pilot-tunnel  System. 

the  center-plane  of  the  pilot;  the  material  in  the  roof  and  sides 
being  held  up  by  an  outer  plate-iron  shell,  made  of  flanged  seg- 
ments and  supported  by  radial  struts  abutting  upon  the  shell  of 
the  pilot  tube.  The  masonry  lining  is  put  in  place  by  setting  up 
ribs  of  T-iron,  curved  to  fit  the  intrados  of  the  arch  and  with  al- 
lowance made  for  the  lagging.  These  center-ribs  are  also  sup- 
ported by  struts  leading  to  the  pilot,  and  the  roof-struts  are 
removed  as  these  are  put  in  place.  In  putting  in  the  outer 
shell-plates,  work  is  commenced  at  the  top  and  the  material  is 


PRINCIPLES  OF  TUNNEL  TIMBERING  AND  DRIVING 


93 


held  back  by  light  poling-boards  until  the  plates  can  be  bolted 
to  the  completed  shell.  This  outer  shell,  which  is  extended 
over  one-third,  or  a  little  more,  of  the  perimeter  of  the  tunnel, 
is  left  in  place. 

Sewer  Tunnel  in  Quicksand — In  building  a  sewer  in  Roches^ 
ter,  N.  Y.,  the  contractor  found  it  necessary  to  drive  a  500- foot 
tunnel  through  quicksand.  W.  D.  Lockwood,  M.  Am.  Soc. 
C.E.,  describes  as  follows  the  method  pursued:* 

The  heading  was  only  6x6  feet  and  this  was  timbered  as 
shown.  In  the  breast  a  center  leg  was  sometimes  employed, 
and  in  other  cases  a  false  cap  and  raker  was  put  in,  tying  up 
the  completed  work  with  stretchers. 

The  sets  were  placed  about  4^  feet,  c.  to  c.,  using  8  x  8-inch 
hemlock,  with  6-foot  oak  lagging,  2  inches  thick  on  the  top, 
and  2-inch  hemlock  lagging  on  the  sides.  Two  miners  in  the 


Longitudinal  Section,  Showing  Methods  of  Timbering. 

FIG.   38. — Sewer-tunnel   in   Quicksand:     Rochester,    N.   Y. 

breast  and  two  muckers  constituted  the  working  force,  and  the 
average  progress  made  was  4^  feet  per  shift.  The  miners  were 
paid  $2.50  per  day  and  the  muckers  $2.00.  The  work  of  driv- 
ing and  timbering  the  tunnel  complete  cost  $5  per  lineal  foot, 
$3  of  this  being  for  labor. 

^Engineering  News,  Feb.  21,  1895. 


94 


MODERN    TUNNEL    PRACTICE 


Dry  Sand  Tunneling. — Dry  sand  will  run  almost  like  a  fluid ; 
and  as  a  consequence  tunneling  through  it  is  slow  and  danger- 
ous work,  requiring  the  utmost  care  and  patience  in  timbering 
to  prevent  a  run  of  sand.  Small,  loose,  dry  gravel  acts  in  much 
-the  same  way. 

In  the  case  of  a  large  sewer  tunnel  through  very  dry  sand, 
built  some  years  ago  in  Brooklyn,  the  sand  flowing  into  the  ex- 
cavation undermined  adjoining  houses,  and  the  job  was  aban- 
doned by  several  contractors  in  succession.  The  then  firm  of 


'- 


—  •**    f—  ;•  

i      3f 

//4            tx>  5'*'  -- 

!t|        > 

!.... 

\l    " 

•   ._ 

.,  ,  M~~    ~~^7v~\a 
/       /  5ect/bns  ra/yanq    \  •              \ 
/  Iron  Bracesare  'made  ;  •                V.\ 
/      to  ao  in  any  Section.  •   '•                 •»  \ 

^ 

r5w^ 


!/2i'/2 


Longitudinal  Section.  Cross  Section. 

FIG.  39. — Temporary  Bracing  of  Old  Tunnel. 

Anderson  &  Barr,  of  New  York,  carried  out  the  work  success- 
fully as  follows : 

A  connection  was  made  with  the  city  water  distribution  sys- 
tem, and  a  large  pipe  was  carried  into  the  tunnel  and  near  the 
working  face  of  the  tunnel.  To  this  water  pipe  was  connected 
by  a  flexible  hose  a  section  of  2-inch  pipe,  about  16  feet  long, 
plugged  at  the  end  and  perforated  at  the  sides  for  a  length  of 
about  10  feet.  By  means  of  this  simple  apparatus  the  dry  sand 
in  the  advance  heading  was  made  wet  enough  to  stand  during 
excavation;  and  a  wall  of  wet  sand  was  thus  continually  kept 
between  the  dry,  running  sand  and  the  finished  tunnel. 


PRINCIPLES  OF  TUNNEL  TIMBERING  AND  DRIVING 


95 


Enlarging  Tunnel  in  Soft  Ground. — In  1894  the  Boston, 
Revere  Beach  and  Lynn  Railroad  Company  was  forced  to  re- 
place an  old  and  narrow  single-track  tunnel  by  a  twin  tunnel 
adapted  to  the  requirements  of  modern  traffic.  The  old  tunnel 
was  471  feet  long,  12^  feet  wide  and  14  feet  high  in  the  clear, 
and  the  material  penetrated  by  it  was  a  clay  hardpan  of  IT 
treacherous  nature.  Mr.  George  M.  Tompson,  M.  Am.  Soc. 
C.E.,  Chief  Engineer,  devised  the  plan  of  reconstruction  here 
briefly  described : 

Though  the  three-ring  brick  arch  of  the  old  tunnel  had  been 
badly  squeezed  out  of  shape  by  the  ground  pressure,  it  was 
determined  to  build  the  new  north  tunnel  parallel  to  the  old 


.* — r.r        , 

FIG.  40. — Section  of  New  Tunnel  Excavation,  Showing  Drifts  and  Bracing. 

tunnel,  complete  the  new  tunnel  and  turn  the  traffic  into  it 
while  building  the  new  south  tunnel. 

The  old  tunnel  was  first  braced  up  with  old  rails  bent  to  form 
as  shown  in  Fig.  39.  This  work  was  done  at  night,  and  the 
upper  sections  were  forced  and  held  up  by  a  hydraulic  jack 
placed  on  a  flat-car,  while  the  men  were  bolting  on  the  leg  sec- 
tions. The  whole  form  was  then  lowered  to  a  bearing  and 
lagging  was  driven  in  to  fill  the  space  between  the  iron  rails  and 


96 


MODERN    TUNNEL    PRACTICE 


the  brickwork.     To  provide  clearance  this  frame  had  to  be 
sunk  into  the  brickwork  in  some  places. 

The  new  tunnel  was  commenced  from  shafts  sunk  near  each 
end,  and  the  material  was  found  to  be  badly  ruptured,  requir- 
ing the  heavy  timbering  shown  in  Fig.  40.  Work  was  com- 
menced at  each  end  at  the  top  of  the  high  side  or  south  drift, 
and  carried  down  3  or  4  feet  by  driving  sheeting  and  poling- 
boards.  The  short  temporary  timbers  were  put  in  and  the  drift 
was  closed  by  a  bulkhead  to  prevent  caving.  The  excavation  in 
this  drift  was  then  carried  down  to  a  point  just  below  the  base 


•— 1~ 


~:     .  _J_J 

iCff  Diortt     '  tT^./i   Klevuc. 


"already  inPiace'-'' 
FIG.  41. — Timber-core  Used  in  Rebuilding  Old  Tunnel. 

of  the  rail  and  the  long  side  timber  was  set.  The  north  drift 
was  then  driven  and  timbered,  and  the  arch  area  was  enlarged 
from  the  upper  central  drift  shown.  The  timber  sets  were 
spaced  3  feet,  c.  to  c. 

After  the  north  tunnel  had  been  completed,  a  heavy  timber 
center  platform  was  built  (Fig.  41)  to  replace  the  earth  core 
used  in  the  new  tunnel  and  not  removed  until  the  arch  had  been 


PRINCIPLES  OF  TUNNEL  TIMBERING  AND  DRIVING  97 

built.  A  drift  was  then  run  over  the  old  brickwork  and  the 
arch  was  broken  through  from  above.  The  new  lining  was  five 
rings  thick. 

Sewer  Tunnel  in  Sand — In  connection  with  the  construction 
of  the  New  York  Rapid  Transit  Railway  a  sewer  tunnel  harhto 
be  driven  under  Chatham  Square.  The  depth  below  the  surface 


a. 

"Jacking  in" 
of   Lagging. 


W "Tile  Drain 

<C"      --.. 

Cantilever 

b-  in     PJace. 

Isometric   View  and 
Section   of   Continuous   Lagging. 


.  1 

•  :^M 


VWDrvinJim 


Sheeting    and    Bracing; 
Arch  Turned  ready  for  Advancing  Heading. 


Method   of    Sheeting 
and    Bracing. 


FIG.  42. — Chatham  Square,  New  York:  Driving  a  Sewer  Tunnel  Through 

Sand. 

was  only  30  feet,  and  the  street  traffic  was  heavy  above  the 
tunnel.  The  material  was  a  fine  running  sand. 

In  driving  this  tunnel,  6-J  feet  diameter,  several  novel  de- 
vices were  made  use  of  which  may  be  summarized  as  follows : 

( i )  The  use  of  a  system  of  interlocking  poling-boards  to 
support  the  roof,  and  the  driving  of  these  boards  by  ratchet- 


v  98  MODERN    TUNNEL    PRACTICE 

jacks.  (2)  The  use  of  a  cantilever  beam  to  support  the  for- 
ward ends  of  the  poling-boards.  (3)  The  support  of  the  sides 
and  front  of  the  excavation  by  lagging  boards  laid  flat  against 
and  over  strips  of  canvas,  the  latter  being  rolled  down  as  the 
excavation  progresses. 

The  poling-boards  were  made  of  3^  x  Q-inch  lagging,  with  a 
3  x  ^-inch  steel  strip  lapping  with  half  its  width  over  the  adja- 
cent board  and  thus  closing  the  space  between  them.  In  the 
bottom  of  these  boards  a  series  of  openings,  guarded  by  cast- 
iron,  are  used  in  pushing  the  boards  forward.  The  power  to 
perform  the  forward  movement  is  supplied  by  a  ratchet  screw- 
jack,  acting  upon  the  board  by  means  of  a  vertical  lever,  and 
reacting  against  the  masonry  lining. 

In  operation  these  boards  are  pushed  ahead  one  by  one,  until 
they  have  been  extended  their  full  length.  When  pushed  for- 
ward there  is  a  very  considerable  downward  pressure  from  the 
earth  above.  To  resist  this  the  load  is  carried  on  transverse 
I-beams  carried  'by  a  cantilever  beam  system,  wedged  up 
against  the  lining  masonry,  as  shown  in  Fig.  42-6. 


CHAPTER  VI 

TUNNEL  ARCH   CENTERING 

Requisites  of  a  good  arch-center — Manner  of  framing  centers — Adjustable 
and  moving  centers — Steel-rib  centers — Concrete-forms  for  small  tun- 
nels— The  placing  of  concrete  tunnel-lining. 

After  the  arch-area  has  been  fully  excavated  and  the  roof 
secured  by  the  necessary  timbering,  a  center,  or  form,  is  re- 
quired Yipon  which  to  build  the  final  protecting  arch  masonry. 
The  principles  of  good  center  design  are :  That  the  completed 
form  has  a  central  opening  sufficiently  large  to  permit  the  pass- 
age of  material  through  it ;  that  the  center  is  strong  enough  to 
hold  the  arch  and  a  possible  load  thrown  upon  it  by  the  ground 
above;  that  it  is  convenient  to  set  up  and  take  down,  with  no 
single  part  too  bulky  or  too  heavy  for  easy  handling,  and  while 
it  should  contain  no  superfluous  material,  it  should  be  so  de- 
signed that  it  will  admit  of  rapid  and  effective  strengthening 
when  an  emergency  arises. 

In  the  United  States  general  use  is  made  of  the  skeleton-rib 
center.  This  is  constructed,  according  to  span  and  load,  of  two, 
three  or  more  layers  of  heavy  plank,  sawed  into  segments  with 
radial  joints  and  with  the  outer  edges  of  the  planks  curved  to 
fit  the  intrados  of  the  arch,  less  the  thickness  of  the  lagging  to 
be  used.  These  segments  are  so  assembled  as  to  "break  joints," 
and  they  are  firmly  fastened  together  with  screw-bolts  so  as  to 
form  a  continuous  rib.  This  rib  is  generally  stopped  some  dis- 
tance above  the  true  spring  of  the  arch ;  the  first  two  or  three 
feet  of  the  arch  being  built  up  by  hand- forms.  The  object  of 
this  is  twofold  ;  the  weight  and  size  of  the  rib  is  thus  reduced, 
and  the  masonry  is  more  easily  started  in.  a  clear  space.  When 
the  center  ribs  are  heavy,  the  joints  are  often  strengthened  by 

99 


100 


MODERN    TUNNEL    PRACTICE 


plate-iron  pierced  with  the  necessary  number  of  holes  for  the 
screw-bolts. 

Fig.  43  shows  the  standard  arch-rib,  lagging  and  supports 
adopted  for  the  tunnels  on  the  Cincinnati  Southern  Railway  in 
1902.  The  vertical  posts  are  made  of  8  x  8-inch  stuff  set  3  feet 
apart  on  centers  and  they  rest  on  short  sills.  On  the  posts  is  a 
4  x  8-inch  wall-plate  mortised  onto  the  head  of  the  posts,  and 
this  wall-plate  carries  the  wedges  which  support  the  rib.  By 
"striking"  these  wedges  after  the  masonry  has  been  laid  and  the 


Cross      Section. 

FIG.  43.— Cincinnati  Southern  R.  R.  Standard  Tunnel  Centering. 

mortar  is  set,  the  rib  can  be  lowered  and  removed  for  re-use.  In 
this  case  the  rib  segments  are  held  together  bv  iron  straos  and 
f-inch  bolts  at  each  joint.  At  the  springing  line  on  each  side, 
short  8  x  8-inch  blocks  are  fitted  between  the  rock  and  the 
wall-plates,  at  each  rib;  these  are  intended  to  hold  the  rib  and 
the  wall-plate  in  true  position  while  the  masonry  is  being  laid. 
These  blocks  are  removed  with  the  centers,  and  the  holes  are 
filled  up  with  brick  laid  in  cement  mortar. 

This  centering  was  built  in  sections  from  10  to  30  feet 
long,  and  it  was  usually  "struck"  in  from  four  to  eight  days 
after  the  completion  of  the  brickwork  lining. 


TUNNEL    ARCH     CENTERING 


101 


Adjustable  or  Moving  Center. — As  before  mentioned  a  number 
of  American  tunnels  were  originally  timber-lined,  with  the  view 
of  hastening  the  completion  of  the  tunnel.  In  time  it  is  neces- 
sary to  re-line  these  tunnels  with  a  more  permanent  material, 
and  this  must  be  done  with  as  little  interference  as  possible  with 
traffic. 

The  illustration,  Fig.  44,  shows  the  plan  adopted  for  re-lin- 
ing a  i,4io-foot  single-track  tunnel  on  the  Clinch  Valley  Divi- 
sion of  the  Norfolk  and  Western  Railway,  this  work  being 


-ff/fe  of.  Three  Thicknesses 

60?  whokKbhalf'circlet 
TO' Radius  when  Lading 
is  on. 


Longitudinal       Section. 
Cross      Section . 

FIG.  44. — Norfolk  &  Western  R.  R.  Adjustable  Centering  Used  in  Relining 

Tunnel. 

done  under  the  direction    of  Charles    S.    Churchill,  M.  Am. 
Soc.  C.  E.* 

The  old  tunnel-lining  was  made  up  of  centers  3  feet  apart, 
located  as  shown  by  the  dotted  lines.  It  was  decided  to  re- 
place this  wooden  lining  with  brick  masonry.  The  rock  roof 
was  bad,  showing  seams  or  breakage  lines  extending  from  I 
foot  to  12  feet  above  the  timbering.  This  dangerous  condition 
made  it  advisable  to  remove  only  a  short  section  of  the  timber- 

*  Engineering  News,  March  22,  1900. 


TO2 


MODERN    TUNNEL    PRACTICE 


ing  at  one  time ;  and  it  was  also  essential  to  close  the  opening 
made  as  quickly  as  possible  with  the  brick  masonry. 

To  meet  these  conditions  the  movable  center  was  made,  as 
shown  in  Figs.  44  and  45.  Two  side  trestles,  with  braced 
posts,  sill  and  cap,  were  built  to  carry  the  moving  centers,  and 


FIG.  45. — Detail  of  Set-screws  and  Rollers. 

two  sections  of, the  trestles  and  centers  were  employed  alter- 
nately. One  set  was  carried  ahead  and  set  for  the  removal  of 
the  old  timbering,  while  the  masons  were  laying  brick  on  the 
other.  The  centers  were  moved  ahead  on  the  rollers  shown  in 
Fig.  45,  and  they  were  "set  up"  and  "struck"  by  means  of  the 
set-screws. 

In  re-lining  the  Boulder  tunnel,  in  1893,  on  the  Montana 
Central  Railway,  another  form  of  movable  center  was  used 
and  is  here  shown  in  Fig.  46.  This  tunnel  was  6,112  feet  long 
and  was  driven  through  a  seamy  blue  traprock,  and  a  mass  of 
boulders  filled  in  with  disintegrated  material.  To  replace  the 
old  timber-lining,  granite  rubble  side  walls  were  built,  13  feet 
high  and  generally  20  inches  thick,  and  the  arch  was  a  full 
center  of  four  rings  of  brick,  with  a  clear  span  of  15.66  feet  at 


TUNNEL    ARCH    CENTERING  ICT} 

the  spring.  Where  greater  strength  was  needed  the  walls  were 
made  30  inches  thick  and  the  arch  was  increased  to  six  rings  of 
brick. 

Owing  to  falls  and  slips  it  was  impossible  to  remove  all  of 
the  old  timbering  as  a  preliminary  to  laying  up  the  side  walls. 
The  plan  followed  was  to  remove  the  old  posts  by  first  support- 
ing the  original  roof  segments  and  the  lagging  and  packing 


Cross  Section . 


Lonqitudinal  Section. 


Cross  Section. 


Longitudinal  Section. 
FIG.  46. — Movable  Arch-centers ;  Boulder  Tunnel:     Montana  Central  R'y- 

above  them,  by  means  of  the  temporary  inclined  posts  shown. 
In  a  longitudinal  section,  of  four  arch-ribs,  covering  a  length  of 
8  feet,  the  first  and  fourth  rib  were  thus  supported,  and  to  hold 
the  two  intermediate  ribs  against  downward  pressure,  6x6- 
inch  struts  were  set  up  under  the  ribs  longitudinally,  and  4x6- 
inch  cross  struts  were  put  in  place  to  resist  lateral  movement. 
The  two  hip-segments  were  then  sawed  off  below  the  connec- 


IO4  MODERN    TUNNEL    PRACTICE 

tion  with  the  temporary  posts  and  the  old  side  timbers  were 
removed  and  the  side  walls  built.  Two  small  derricks — fixed 
on  the  flat-cars  which  brought  the  stone  into  the  tunnel — were 
used  in  laying  these  walls. 

The  brick  arch  was  laid  on  a  center  running  on  rollers,  on 
sills  laid  at  the  foot  of  the  side  walls,  this  center  being  fitted 
with  screw-jacks  to  raise  and  lower  it.  This  center  was  5^ 
inches  less  in  diameter  than  the  distance  between  the  side  walls, 
thus  permitting  the  use  of  2f-inch  lagging.  Each  center  was 
made  up  of  three  ribs  constructed  of  i-inch  or  2-inch  board 
segments,  and  each  rib  was  10  inches  thick  and  14  inches  deep, 
the  planks  being  well  bolted  together.  As  the  ribs  were  4  feet 
apart  the  total  length  of  one  center  was  about  9  feet. 

The  arch  was  built  up  from  the  spring  on  both  sides  at  once, 
by  four  masons,  and  all  the  space  between  the  arch  and  the  rock 
was  securely  packed  with  dry  rubble.  As  soon  as  the  arch  work 
had  been  carried  high  enough  to  give  the  hip-segments  a  bear- 
ing of  a  foot  or  more  on  the  masonry,  these  segments  were 
securely  wedged  and  blocked  up  against  the  brickwork,  and  the 
longitudinal  4  x  6-inch  timbers  were  removed.  The  arch  was 
then  completed,  the  keying  being  done  by  two  masons,  begin- 
ning at  the  completed  end  and  working  back  toward  the  end  left 
"toothed"  for  the  next  section  of  the  arch.  A  staging-car  was 
used  in  building  this  brickwork. 

A  single  crew  of  brick  and  stone  masons  completed  8  lineal 
feet  of  arch  and  side  walls  in  24  hours ;  the  timber  and  trim- 
ming crews  were  at  work  at  the  same  time  preparing  for  the 
brick  and  stone  laying  crews.  Including  an  engine  and  two 
train  crews  35  men  were  employed  in  this  work. 

The  Musconetcong  tunnel  was  built  in  1872-75,  and  in  1899 
it  became  necessary  to  line  the  portions  of  it  originally  left  un- 
lined,  owing  to  infiltration  of  water  and  unreliable  rock.  This 
re-lining  had  to  be  done  without  interrupting  traffic,  and  plans 
were  made  accordingly.  Owing  largely  to  the  unevenness  of 
the  rock  roof,  concrete  was  adopted  as  the  material  to  be  used ; 
with  a  minimum  depth  of  18  inches  at  the  key  and  24  inches  at 
the  springing  line  and  for  the  thickness  of  the  side  walls. 


TUNNEL    ARCH    CENTERING 


105 


To  facilitate  the  passing  of  trains  in  this  double-track  tunnel 
a  gauntlet  track  was  first  arranged  through  the  tunnel,  provid- 
ing a  working  space  at  each  side  wall.  In  these  spaces  a  2-foot 
gauge  track  was  laid,  by  using  the  outside  rails  of  the  gauntlet 
as  one  of  the  rails  of  these  tracks.  The  concrete  platform  was 
erected  outside  the  east  portal,  at  the  height  of  a  car-floor  above 
the  head  of  the  rail. 

The  traveler  used  in  preparing  the  roof  for  the  lining  was 
constructed  as  in  Fig.  47,  and  it  ran  on  two  rails  laid  close  to 


End      Elevation.  Sicfa         Elevation.  u»>** 

FIG.  47. — Musconetcong  Tunnel :  Traveling  Arch-center. 

the  side  walls.  The  timber  was  hard  pine,  and  the  wheels  were 
double-flanged.  The  cross-beam  indicated  carried  the  wofking 
floor  for  the  men,  and  was  sufficiently  high  to  permit  the  pass- 
age of  trains  beneath. 

To  put  in  the  concrete  arch  the  rock  roof  was  hand-drilled 
and  blasted;  the  sides  were  blasted  out  ahead  of  the  traveler, 
40%  dynamite  being  used,  so  as  not  to  shake  up  the  rock  any 
more  than  was  necessary.  In  the  case  of  heavy  roof  shots,  the 
traveler  was  run  out  of  the  way  and  the  track  was  protected  by 
ties.  In  from  10  to  20  minutes  after  a  shot  the  track  was 
cleared  of  all  debris  and  the  traffic  was  never  delayed. 

The  side  walls  were  built  by  first  setting  up  the  temporary 
posts,  then  lagging  up  for  a  few  feet,  and  depositing  the  con- 
crete in  the  space  behind.  When  the  concreting  had  reached 
the  springing  lines,  and  was  set,  the  posts  and  lagging  were  re- 
moved and  thinner  posts  were  substituted;  on  the  latter  were 
laid  the  wall-plates  for  supporting  the  iron  ribs  and  the  2-inch 


IO6  MODERN    TUNNEL    PRACTICE 

lagging.  These  iron  ribs  were  made  in  halves,  bolted  together 
at  the  crown,  and  the  foot  of  each  rested  on  a  cast-iron  sand-box 
fitted  with  a  screw  plug.  A  1 6- foot  section  was  concreted  at 
one  time  at  the  sides,  and  a  lo-foot  section  at  the  roof.  As  the 
arch  concreting  approached  the  crown,  stiff  struts  were  put  in 
between  the  ribs  and  the  rock  roof  to  keep  the  sides  from  rising 
at  the  key,  owing  to  the  heavy  load  on  the  haunches.  Where 
the  drip  of  water  from  the  roof,  or  the  flow  of  water  from  the 
sides,  was  heavy,  a  3-inch  pipe  was  buried  in  the  concrete  ex- 
tending clear  through  to  the  rock. 

The  cost  of  this  re-lining  was  $54  per  lineal  foot  of  tunnel 
lined,  including  blasting,  mucking,  concreting,  handling  ma- 
terials, supplies  and  workmen.  To  this  must  be  added  $29.91 


FIG.  48. — New  York  Subway :  Method  of  Roof-timbering. 

per  lineal  foot  for  a  charge  for  temporary  spur,  gauntlet  track, 
shanties,  platform,  train  service,  etc.,  making  a  total  cost  of 
$83.91  per  lineal  foot  of  tunnel  lined. 

In  placing  the  concrete  lining  in  the  New  York  Rapid  Tran- 
sit tunnel,  traveling  forms  and  centers  were  used  as  shown  in 
Figs-  5°»  51- 

The  general  section  of  the  tunnel,  and  the  method  of  timber- 
ing the  roof  in  the  Park  Avenue  tunnel,  is  shown  in  Fig.  48. 
The  concrete  footing  courses  of  the  side  walls  were  first  laid, 
these  projecting  inward  about  18  inches  from  the  face  of  the 
wall.  On  these  projections  track  rails  were  laid  on  each  side  of 
the  tunnel  for  carrying  traveling  platforms.  There  were  three 
of  these  platforms;  the  forward  one  (Fig.  49)  was  made  for 


TUNNEL    ARCH    CENTERING 


107 


building  the  side  walls,  a  center  one  carried  a  derrick,  and  the 
third  (Fig.  50)  was  employed  in  building  the  arch. 

Fig.  49  shows  the  construction  of  the  traveler  used  in  build- 
ing the  side  walls.  This  platform  was  mounted  on.  six  wheels 
in.  all,  and  on  each  side  there  was  mounted  an  adjustable  lag^ 
ging,  curved  to  fit  the  profile  of  the  wall.  In  operation  this 
platform  was  rolled  to  place,  and  the  lagging  adjusted  to  posi- 
tion and  held  by  wedges.  Skips  of  concrete  were  then  hoisted 
onto  the  platform  and  the  concrete  was  shoveled  into  the  space 
between  the  lagging  and  the  rock  and  rammed  until  it  reached 
the  top  of  the  lagging.  When  the  concrete  had  set,  the  wedges 
were  loosened  and  the  platform  was  moved  ahead  and  ad- 
justed for  building  a  new  section. 

The  derrick  platform  was  22^  feet  wide  between  center  of 


Part     Side     Elevation. 


Half        Cross        Section. 


FIG.  49. — New  York  Subway :  Platform  for  Building  Side-walls. 

track  wheels  and  was  18  feet  long  over  all.  Transversely  it  was 
divided  into  three  bays,  the  center  bay  being  unfloored  so  that 
concrete  skips  could  be  hoisted  through  it  from  the  cars  run- 
ning on  a  track  beneath  the  platform.  A  derrick  was  mounted 
at  the  center  of  one  of  the  floored  bays,  and  this  derrick  served 
both  the  side  wall  and  the  arch  platforms. 

The  roof-arch  platform  is  shown  in  Fig.  50.  It  was  practi- 
cally the  same  as  the  side  wall  platform,  with  the  addition  of 
roof-arch  centers  at  each  bent.  The  top  of  the  completed  side 
walls  reached  the  point  B,  while  the  roof-lagging  commenced 
at  A.  The  space  A  B  was  bridged  by  using  special  sector-like 
forms.  The  concrete  was  shoveled  into  the  arch,  commencing 
at  the  spring  on  both  sides,  until  the  arch  was  too  high  for  con- 
venient handling  from  the  platform.  When  the  throw  became 


loS 


MODERN    TUNNEL    PRACTICE 


TUNNEL    ARCH     CENTERING 


IOQ 


excessive,  the  concrete  was  shoveled  from  the  skip  onto  the 
small  platform  C  D,  and  then  into  the  arch. 

When  the  two  sides  approached  within  5  feet  of  each  other 


FIG.  51. — New  York  Subway:  Side-wall  Mold. 

at  the  crown,  this  key  was  built  in  by  working  from  the  rear 
forward. 

In  certain  sections  of  the  New  York  Subway  the  side  wall 


FIG.  52. — Steel  Arch-center:  East  Boston  Tunnel. 

mold  was  made  as  shown  in  Fig.  51.    This  was  mounted  on  the 
traveling  platform  already  described  in  Fig.  50. 

Steel-rib  Center — In  building  the  East  Boston  tunnel,  an  ex- 
tension of  the  Boston  Subway,  a  steel  rib  was  employed  to  sup- 


110  MODERN    TUNNEL    PRACTICE 

port  the  lagging  used  in  building,  the  concrete-steel  lining.  The 
clear  dimensions  of  this  tunnel  were  20.5  feet  high  by  23.3  feet 
wide,  and  the  steel-rib  support  was  devised  to  facilitate  the 
rapid  transport  of  all  debris  out  of  the  tunnel,  and  concrete  into 
it.  The  ribs  were  made  of  curved  steel  beams  riveted  and 
braced  together,  and  on  the  cross  tie-beams  provided  a  platform 
was  laid  containing  a  track  for  the  concrete  cars.  The  muck 
cars  ran  on  the  two  lower  tracks. 

Steel  Traveling  Shields — The  Moncreiffe  Tunnel,*  England, 
has  been  recently  enlarged  from  a  single  to  a  double  track  sec- 
tion, the  traffic  being  meanwhile  maintained  on  the  single-track 
line  in  the  center  of  the  tunnel.  The  work  of  reconstruction 
was  done  by  means  of  four  steel  traveling  shields,  designed  as 
follows : 

Each  shield  was  32  feet  long,  divided  into  9  ribs,  and  each  rib 
was  made  of  a  curved  channel  (9x4  inches)  shaped  to  fit  the 
inner  section  of  the  new  masonry.  Inside  this  channel  member 
were  two  vertical  posts  and  a  horizontal  top  beam  arranged  to 
leave  a  clear  rectangular  space  for  the  passage  of  trains,  13  feet 
8  inches  wide  and  13  feet  6  inches  high.  The  external  width 
of  the  shield  itself  was  22  feet,  and  the  height  was  16  feet  8 
inches.  The  vertical  posts  and  the  outer  channels  were  latticed 
together,  and  two  inclined  members,  reaching  from  the  crown 
point  to  the  springing  point  on  each  side,  tied  the  posts,  horizon- 
tal beam  and  outer  channels  together.  The  shield  was  tied  to- 
gether longitudinally  by  beams  and  cross  braces  between  the 
ribs. 

The  feet  of  the  outer  channel  and  the  inner  posts  were  car- 
ried on  four  sets  of  longitudinal  steel  beams ;  under  these  beams 
were  four  sets  of  cast-iron  wheels,  and  between  these  beams, 
on  each  side,  was  a  clear  space  of  2  feet  3  inches  to  permit  the 
passage  of  narrow  iron  cars  running  on  a  separate  track  of 
13-inch  gage  and  used  for  bringing  in  supplies  and  transport- 
ing waste  material. 

In  operating  this  shield  the  side  rock  was  excavated  and  the 

^Proceedings  of  The  Institution  of  Civil  Engineers ;   Vol.   CLXI,   Sep- 
tember, 1905. 


TUNNEL    ARCH    CENTERING  lit 

side  walls  were  built  in  advance.  The  shield  was  then  used  as  a 
staging  for  the  workmen  for  dealing  with  the  arch  portion,  and 
as  a  protection  to  the  traffic  on  the  railway.  The  unlined  por- 
tions of  the  old  tunnel  were  reconstructed  in  lengths  of  12  feet, 
so  that  the  32-foot  shield  projected  5  feet  under  the  previously- 
built  new  arch  and  15  feet  under  the  old  arch,  thus  giving  an 
ample  margin  of  protection.  Where  crown-bars  had  to  be  used 
to  prevent  the  fall  of  large  pieces  of  loose  rock  in  the  roof,  these 
bars  were  supported  by  posts  resting  upon  the  steel  ribs.  When 
the  necessary  rock  excavation  had  been  completed,  ordinary 


FIG.  53. — Method  of  Setting  Form  for  'Concrete  Invert. 

wooden  tunnel  centers  were  used  for  building  the  new  arch, 
located  in  the  rear  of  the  steel  shield. 

Concrete  Form  for  Small  Tunnel — The  form  illustrated  in  Fig. 
53  was  used  in  laying  the  concrete  invert  foundation  in  the  Cin- 
cinnati Water  Works  tunnel.  The  concrete  was  laid  in  1 6-foot 
sections,  the  forms  being  set  4  feet  apart.  The  interest  in  this 
form  chiefly  lies  in  the  simple  manner  devised  for  holding  the 
form  in  place. 

After  the  brick  invert  had  been  laid  on  this  concrete  founda- 
tion, the  brick  arch  was  built  on  lagging  supported  on  ribs  made 
of  two  3  x  4  x  f -inch  angles,  bent  to  form  and  riveted. 


CHAPTER  VII 

.  .  \ 

SUB-AQUEOUS    TUNNELS    AND    TUNNEL    SHIELDS 

Introduction — Form  of  shield  and  method  of  driving  at  East  Boston  Sub- 
way— The  East  River  gas  tunnel — Massachusetts  pipe-line  tunnel — 
Blackwell  tunnel — St.  Clair  tunnel — Berlin-Spree  tunnel — Harlem 
River  tunnel — Pennsylvania  R.  R.  Hudson  River  tunnel — Screw-jack 
shield — Shankland  shield. 

Tunnels  of  the  type  here  discussed  are  usually  located  under  a 
waterway  separating  parts  of  one  city,  or  are  found  on  lines  of 
railway  where  it  is  deemed  more  economical  and  as  better  meet- 
ing the  demands  of  general  traffic,  to  tunnel  under  the  water- 
way rather  than  to  bridge  it.  Where  rock  is  found  in  tunnels 
of  this  description,  the  line  of  the  tunnel  is  necessarily  so  near 
to  the  surface  of  the  rock  that  the  work  is  liable  to  be  seriously 
interfered  with  by  the  occurrence  of  vertical  seams  filled  with 
decomposed  rock  and  communicating  with  the  water  above. 
And  when  the  material  penetrated  is  other  than  rock  it  is  an 
alluvial  deposit  also  more  or  less  water-bearing. 

Conditions  of  traffic — as  well  as  those  of  construction — re- 
quire that  these  sub-aqueous  tunnels  be  located  as  near  to  the 
water-level  as  the  depth  of  water  in  the  channel  and  the  nature 
of  the  material  penetrated  will  permit ;  otherwise,  the  gradients 
or  the  length  of  the  tunnel  may  be  excessive  for  the  purposes  of 
construction  or  operation.  Owing  to  these  facts  tunnels  of  this 
nature  are  usually  difficult  to  build,  costly  and  more  or  less  dan- 
gerous to  the  working  force;  and  various  methods  have  been 
devised  to  minimize  the  dangers  to  be  encountered  and  to  facil- 
itate the  work  of  driving  the  tunnel.  Chief  among  these  is  the 
use  of  shields  and  compressed  air,  employed  together  or  sepa- 
rately. As  shields  for  supporting  the  face  and  roof  and  guard- 
ing against  the  inrush  of  material  or  water,  are  an  essential 

112 


SUB-AQUEOUS  TUNNELS  AND  TUNNEL  SHIELDS  113 

feature  of  sub-aqueous  tunneling,   this  chapter  deals  largely 
with  this  engineering  device. 

Historically  considered,  the  first  sub-aqueous  tunnel  of  any 
importance,  and  through  soft  ground,  is  that  under  the  River 
Thames,  in  London.  This  tunnel  was  first  proposed  in  1798, 
by  Ralph  Dodd;  and  in  1807  work  was  actually  commenced 
upon  it  by  the  Cornish  engineer,  Trevithick,  and  a  small  drift 
was  run  under  the  river  for  a  length  of  1,046  feet.  But  as 
some  doubt  had  been  raised  as  to  the  accuracy  of  this  line  in 
direction,  Trevithick  made  an  opening  in  the  top  to  test  his 
position,  with  the  result  that  he  let  in  the  water  and  nearly 
drowned  himself  and  his  party.  The  project  was  taken  up  in 
1824  by  Mark  Isambard  Brunei;  but  again  the  water  broke  in 
and  the  tunnel  was  abandoned  for  a  time. 

Brunei  then  devised  a  sectional  shield  for  protecting  the  ad- 
vance working,  the  first  shield  of  record,  and  by  its  use  the 
tunnel  was  opened  to  foot  passengers  in  1843.  This  original 
Brunei  shield  was  made  up  of  a  strong  iron  framework  built  in 
horizontal  sections  of  a  comparatively  small  depth  that  could 
be  advanced  separately,  and  cut  vertically  into  three  compart- 
ments. The  sections  were  advanced  by  powerful  screw-jacks, 
and  the  vertical  face  was  protected  by  horizontal  poling-boards 
that  could  be  handled  separately  and  pushed  forward  as  the 
ground  was  excavated.  The  brickwork,  covering  two  arches 
of  1 4- foot  span  each,  was  built  behind  the  shield  as  this  ad- 
vanced. This  Thames  tunnel  was  1,300  feet  long,  and  in  its 
extreme  dimensions  it  was  35  feet  wide  and  20  feet  high. 

Hydraulic  rams  for  pushing  forward  the  shields,  and  a  per- 
manent iron  lining  in  which  to  lay  the  masonry,  were  probably 
first  used  in  1868-69  m  building  an  8- foot  tunnel  under  the 
Thames ;  the  next  prominent  use  of  the  hydraulic  jack  was  in 
the  10- foot  tunnel  of  the  City  and  South  London  Subway,  com- 
pleted in  1890;  and  jacks  of  this  type  were  used  on  a  large 
scale  on  the  Blackwell  tunnel  of  1890,  and  the  20- foot  St.  Clair 
tunnel  of  1892,  and  in  the  Paris  sewer  tunnels  of  1896.  Since 
these  dates  the  use  of  shields  has  been  extended  in  many  coun- 
tries, and  the  development  of  this  process  of  excavation  is  best 


114  MODERN    TUNNEL    PRACTICE 

noted  by  the  description  of  typical  actual  modern  work  of  this 
class. 

Blackwell  Tunnel — This  tunnel  under  the  Thames,  completed 
in  1895,  is  27  feet  diameter,  making  it  the  largest  sub-aqueous 
tunnel  built  to  that  date.  The  material  penetrated  was  chiefly 
water-bearing  sand,  loose  gravefand  some  good  clay.  At  one 
point  in  its  length  only  5  feet  of  so-called  "ballast,"  or  small 
water- worn  stone,  covered  the  roof  of  the  tunnel ;  and  at 
this  point  clay  was  dumped  to  a  depth  of  10  feet  and  150  feet 
in  width,  to  protect  the  workmen  from  an  inrush  of  water.  The 
river  portion  of  the  Blackwell  tunnel  is  1,212  feet  long. 

The  shield  here  used  was  chiefly  remarkable  for  its  unusual 
size  and  its  somewhat  complicated  design.  As  shown  in  Fig, 
54,  this  shield  was  circular  in  form,  28  feet  8  inches  in  outside 
diameter  and  it  was  19  feet  6  inches  long  over  all;  it  weighed 
230  tons.  The  outside  shell  was  made  of  four  f-inch  steel 
plates,  and  the  interior  was  divided  and  the  shell  stiffened  by 
two  vertical  diaphragms,  25^-  inches  apart.  The  space  between 
these  diaphragms  was  to  be  used  as  an  air-lock  should  condi- 
tions demand  a  greater  air-pressure  at  the  working  face  than 
at  the  rear  of  the  shield ;  but  there  was  no  occasion  to  employ 
this  differential  pressure.  The  material  excavated  at  the  face 
was  passed  through  these  diaphragms  by  chutes  provided  with 
doors  at  each  end  and  acting  as  air-locks. 

Horizontally,  the  forward  part  of  the  shield  .was  divided  by 
three  platforms,  forming  four  working  stages  for  the  men. 
The  three  longitudinal  and  vertical  partitions  cut  the  face  into 
twelve  compartments  and  also  acted  as  stiffeners.  About  6^ 
feet  back  from  the  cutting  edge,  in  each  one  of  these  twelve 
compartments,  a  vertical  cross  screen  was  introduced,  about  30 
inches  in  depth  from  the  top;  these  screens  being  intended  to 
form  a  place  of  refuge  for  the  men  in  case  of  an  inrush  of 
water,  as  the  air  in  these  closed  places  would  keep  them  from 
filling  with  water. 

The  shield  was  pushed  forward  by  28  loo-ton  hydraulic 
jacks  abutting  against  the  cast-iron  tunnel  lining  inside  the  rear 
hood.  This  tunnel  lining  was  very  heavy,  each  segment  weigh- 

7,  if*/      <£e«j   f+    ^     6   m  ^ 

?^>        'p'.-ft- 


SUB-AQUEOUS  TUNNELS   AND  TUNNEL  SHIELDS  I  15 


FIG.  54.— Hydraulic  Shield  and  Lock :  Blackwell  Tunnel  Under  the  Thames. 


Il6  MODERN    TUNNEL    PRACTICE 

ing  about  one  ton — and  two  hydraulic  "erectors"  were  used  to 
lift  and  hold  up  a  segment  until  it  could  be  bolted  to  the  seg- 
ments in  place. 

This  shield  proved  unwieldy,  and  after  about  125  feet  of  the 
tunnel  had  been  driven  with  it  the  cutting  edge  encountered 
a  boulder  in  the  sand  and  was  bent  upward  at  the  bottom.  The 
shield  was  pushed  forward  about  192  feet  further,  but  it  then 
became  so  damaged  as  to  be  useless.  As  it  could  not  be  with- 
drawn, it  was  forced  forward  to  the  next  shaft  by  driving  a 
timber  advance  bottom-heading,  and  laying  down  in  this  a 
concrete  bed  upon  which  the  shield  could  slide,  the  injured  part 
being  thus  relieved  of  strain. 

St.  Clair  Tunnel. — This  tunnel  passes  under  the  river  of  the 
same  name  connecting  Lakes  Huron  and  Erie.  The  tunnel  is 
2,465  feet  long  between  centers  of  shore  shafts,  and  is  21  feet 
6  inches  in  outside  diameter.  It  is  located  in  a  bed  of  blue  clay, 
with  the  bottom  of  the  tunnel  about  60  feet  below  water  level, 
and  was  built  inside  a  circular  cast-iron  lining  by  means  of 
a  shield  designed  by  Joseph  Hobson,  the  Chief  Engineer.* 

The  chief  interest  lies  in  the  size  and  form  of  the  shield  used. 
As  here  shown,  this  shield  consisted  of  a  cylindrical  shell,  21 
feet  6  inches  in  external  diameter  and  15  feet  3  inches  long 
over  all.  The  shell  was  made  of  i-inch  steel  plates  butt- jointed 
with  plain  joints;  and  the  segments  forming  the  shield  were 
united  by  double  angles  on  the  interior  face,  riveted  to  the  shell 
and  together.  The  shield  bulkhead  was  placed  four  feet  back 
of  the  rear  end.  It  was  made  of  -|-inch  plate,  with  seven  hori- 
zontal and  three  vertical  stiffening  members.  In  the  lower-- 
part of  this  opening  were  two  openings,  6  feet  high  by  4^  feet 
wide,  passing  the  material  excavated;  these  openings  were 
closed  by  sliding  doors  suspended  by  chains.  But,  as  a  matter 
of  fact,  these  doors  were  never  closed  throughout  the  execution 
of  the  work. 

To  push  the  shield  forward  twenty-four  hydraulic  jacks 
were  installed  in  the  outer  ring.  Each  jack  had  two  cylinders : 

*For  a  detailed  history  of  this  tunnel  see  Engineering  News,  Oct.  4, 
Nov.  8  and  Dec.  20,  1890. 


SUB-AQUEOUS  TUNNELS  AND  TUNNEL  SHIELDS 


FIG.  55. — Longitudinal  and  Transverse  Sections  of  the  Shield  Used  at  the 

St.  Clair  Tunnel. 


n8 


MODERN    TUNNEL    PRACTICE 


one  8  inches  in  diameter,  to  push  the  shield  forward ;  the  other, 
2§  inches  in  diameter,  used  in  drawing  back  the  large  plunger 
to  make  room  for  a  new  set  of  lining  rings.  With  a  hydraulic 
pressure  of  2,000  pounds  per  square  inch,  the  first  set  of  jacks 
exerted  a  force  of  99,000  pounds,  and  the  second  7,250  pounds. 
The  arrangement  of  these  jacks  is  shown  in  the  illustration. 

In  front  of  the  bulkhead  three  vertical  and  two  horizontal 
partitions  were  built,  to  stiffen  the  shell  and  to  serve  as  plat- 
forms for  the  workmen.  Both  sets  of  partitions  stopped 
within  4  feet  of  the  bulkhead,  or  diaphragm,  thus  leaving 
abundant  room  to  throw  the  clay  down  before  the  bottom  open- 
ings ;  these  partitions  were  sloped  back  from  the  face,  as  shown. 

Mr.  Hobson  made  some  calculations  on  the  friction  of  the 


FIG.  56.— Shield  Used  at  Spree  Tunnel,  Berlin. 

cylinder  in  moving  through  fairly  homogeneous  clay.  The 
pressure  used  to  drive  the  cylinder  forward  varied  from  450 
to  2,000  tons,  and  the  area  of  skin  of  the  cylinder  was  1,030 
square  feet  in  contact  with  the  clay.  The  theoretical  friction 
was,  therefore,  about  875  to  3,880  pounds  per  square  foot,  or 
6  to  27  pounds  per  square  inch. 

Berlin  Tunnel  Under  the  Spree. — This  tunnel  is  1,490  feet  long 
under  the  River  Spree,  and  is  13.12  feet  in  outside  diameter, 
lined  with  cast-steel  flanged  rings,  coated  inside  and  out  with 
cement  mortar.  The  tunnel  bottom  lies  about  40  feet  below 
the  mean  water  level,  with  a  least  thickness  of  10  feet  of  soil 
above  the  shell.  The  material  penetrated  was  mud  and  sand, 
heavily  charged  with  water.  The  steel  cylinder  rings  are  2.13 
and  1.64  feet  wide,  and  each  ring  is  made  of  nine  segments 


SUB-AQUEOUS  TUNNELS  AND  TUNNEL  SHIELDS  I IQ 

fitted  with  inside  flanges.  Between  these  rings,  during  erec- 
tion, flat  steel  circles  were  bolted,  extending  outside  the  shell 
and  increasing  the  rigidity  of  the  tube. 


FIG.  57. — Boston  Subway  :  East  Boston  Extension,  Showing  Standard  Con- 
crete Lining  and  Steel  Ribs  Imbedded  in  Concrete. 

The  actual  excavation  was  conducted  under  compressed  air 
and  with  a  shield.     As  shown  in.  Fig.  56,  this  shield  had  a 


I2O  MODERN    TUNNEL    PRACTICE 

double  bulkhead,  with  an  air-lock  passing  through  both;  and 
in  the  rear  of  this  transverse  partition  were  the  hydraulic  jacks. 
In  front  of  the  bulkhead  was  a  hood,  cut  away  at  an  angle  of 
45°,  with  this  oblique  face  closed  by  hinged  doors,  which  may 
be  opened  at  will. 

The  material  removed  through  the  doors  was  thrown  to  the 
bottom  of  the  hood,  where  it  was  removed  by  a  sand-pump  ex- 
tending through  the  bulkhead.  The  advance  hood  was  perma- 
nently closed  at  the  top,  providing  a  space  filled  with  air,  which 
could  be  used  as  a  refuge  by  the  workmen  in  case  of  a  sudden 
rush  of  sand  and  water.  The  air-lock,  placed  in  the  bulkhead, 
is  intended  for  similar  use. 

The  actual  construction  chamber  lay  between  this  shield  and 
a  temporary  transverse  wall,  built  at  some  distance  to  the  rear 
and  fitted  with  two  air-locks,  one  for  men  and  the  other  for 
materials. 

The  steel  rings  were  mounted  under  the  rear  of  the  shield, 
with  some  space  left  between  the  lining  and  the  rear  hood  of 
the  shield.  In  this  annular  space  cement  was  rammed  in  place ; 
this  cement  acting  as  a  protection  to  the  metal  shell  and  also 
as  a  seal  against  sand  and  water  from  without.  In  pushing- 
forward  the  shield  the  sixteen  hydraulic  jacks  acted  against  the 
steel  lining  ring.  This  tunnel  was  completed  in  1899. 

East  Boston  Extension :  Boston  Subway This  tunnel  for  about 

2,250  feet  of  its  length  passes  under  an  arm  of  Boston  Harbor, 
with  1 6  to  1 8  feet  of  earth  over  the  outside  of  the  tunnel 
roof  at  the  deepest  part  of  the  harbor,  where  there  is  35^  feet 
of  water  at  mean  low  tide.  The  material  being  generally 
clay,  but  somewhat  treacherous,  the  construction  called  for  a 
roof-shield.  A  horse-shoe  section  was  adopted  for  the  tunnel, 
(Fig-  57)»  with  a  clear  width  of  23  feet  4  inches,  and  a  clear 
height  of  20  feet  6  inches.  Owing  mainly  to  the  high  cost  of 
iron,  a  concrete  shell  was  built  about  this  tunnel,  2  feet  9  inches 
thick  at  crown  and  sides,  and  2  feet  thick  in.  the  invert.  In 
water-bearing  material  this  shell  was  tightened  and  reinforced 
by  a  cast-iron  shell  of  flanged  and  bolted  segments,  having  steel 
plate  ribs  imbedded  in  the  concrete,  with  cement  grout  forced 


SUB- AQUEOUS  TUNNELS  AND  TUNNEL  SHIELDS  121 

between  the  cast-iron  shell  and  the  grout.    This  construction  is 
also  shown  in  Fig-.  57. 

The  roof-shield  actually  used  on  this  extension  was  semi- 


FIG.  58.— Roof-shield,  Boston  Subway,  East  Boston  Extension;  Front 
Rear  Rib  and  Longitudinal   Section. 


and 


122 


MODERN    TUNNEL    PRACTICE 


circular,  tied  together  at  the  base  by  a  transverse  girder  and 
stiffened  by  vertical  and  diagonal  riveted  plate  and  angles.  It 
is  shown  in  Figs.  58  and  59. 

East  River  Gas  Tunnel — This  tunnel  is  used  for  piping  gas 
under  the  East  River,  and  serves  as  a  typical  illustration  of 
tunneling  in  a  treacherous,  water-bearing  material ;  it  was  built 
in  1894  by  the  East  River  Gas  Company,  under  Mr.  C.  M. 
Jacobs  as  Chief  Engineer. 

From  center  to  center  of  shore  shafts  the  tunnel  is  2,516  feet 


FIG.  59. — Roof-shield:     Boston  Subway;  Half  Front  Elevation  and  Jack- 
connection. 

long;  the  center  of  the  tunnel  is  107  and  119  feet  below  mean 
low  tide,  giving  a  drainage  toward  the  Long  Island  side.  In 
the  solid  rock  the  section  is  10  feet  wide  by  8J  feet  high  at  the 
crown,  and  in  soft  ground  a  cast-iron  shell  (Fig.  60)  is  used, 
10  feet  2  inches  in  diameter  clear  of  flanges.  The  material 
penetrated  was  hard  gneiss  rock  for  the  lower  part  of  the  tun- 
nel ;  but  for  something  over  200  feet  the  tunnel  passed  through 
almost  vertical  layers  of  decomposed  felspar,  a 'greenish,  marl- 
like  formation  that  ran  like  paint  when  wet,  and  loose  rock. 
All  of  this  material  was  water-bearing,  the  vertical  seams  com- 
municating with  the  river  above. 


SUB-AQUEOUS  TUNNELS  AND  TUNNEL  SHIELDS  I2J 

The  hard  rock  portion  was  tunneled  in  the  usual  manner 
without  difficulty;  but  for  the  soft  ground  part  a  shield  and 
iron  lining  were  required,  operated  along  with  compressed  air. 


The 

and 


Go»  Section.  Long,  Section. 

FIG.  60. — East  River  Gas  Tunnel :     Cast-iron  Lining. 

cast-iron  lining  was  10  feet  10  inches  in  outside  diameter 
was  made  in  rings  16  inches  wide,  and  in  nine  flanged  seg- 


Longitudinal  Section., 


End  View  of  Head. 


FIG.  61. — Shield  :  East  River  Gas  Tunnel. 


I24 


MODERN    TUNNEL    PRACTICE 


ments  with  a  key-piece  8  9-32  inches  long.  Every  segment  was 
drilled  for  a  i^-inch  pipe  nipple  for  hose  attachment  to  grout- 
pump.  This  iron  lining  was  chiefly  adopted  because  it  was 
found  that  water  was  forced  through  the  brickwork  first  tried. 
The  shield  is  shown  in  Fig.  61,  planned  by  Mr.  W.  I.  Aims, 
the  engineer  in  charge.  It  weighed  about  twelve  tons,  and  was 
10  feet  f  inches  in  external  diameter  and  7  feet  2.\  inches  long: 
its  general  arrangement  is  shown  in  the  cut.  In  the  annular 
space  indicated  twelve  5-inch  hydraulic  jacks  were  located,  each 
designed  to  work  under  a  hydraulic  pressure  of  5,000  pounds 
per  square  inch,  making  it  possible  to  exert  a  force  of  600  tons 


FIG.  62. — Twin-tube  Tunnel  Under  Harlem  River. 

in  pushing  the  shield  forward.  The  shield  and  heading  were 
lighted  by  incandescent  lamps,  and  were  connected  with  the 
office  above  ground  by  a  telephone. 

As  the  axis  of  the  tunnel  was  120  feet  below  mean  low  tide, 
the  air  pressure  required  ran  from  48  to  52  pounds  per  square 
inch,  a  record  surpassing  that  of  any  other  known  work  con- 
ducted by  the  plenum-pneumatic  process.  Notwithstanding 
careful  physical  examination  of  the  workmen,  and  the  use  of 
every  precaution,  in  leaving  or  entering  the  air-lock,  there  were 


SUB-AQUEOUS  TUNNELS  AND  TUNNEL  SHIELDS 

four  fatal  cases,  due  to  carelessness  in  entering  or  leaving  the 
lock.  The  air-lock  was  of  the  ordinary  construction. 

Harlem  River  Tunnel — This  tunnel  forms  part  of  the  New 
York  Subway  system,  and  it  passes  under  the  Harlem  River, 
with  the  rail-base  44.66  feet  below  mean  high  water ;  the  depth 
of  the  river  is  about  26  feet,  with  a  range  of  tide  of  about  5 
feet.  The  material  penetrated  by  the  tunnel  is  mud,  silt  and 
sand,  the  latter  flowing  with  remarkable  ease  when  wet.  Be- 
tween the  bulkhead  lines  the  river  is  400  feet  wide;  but  for 
610  feet  the  tunnel  is  made  of  two  cast-iron  cylinders,  im- 
bedded in  concrete,  as  shown  in  Fig.  62. 

To  build  this  section  of  tunnel  Mr.  D.  D.  McBean,  of  the 
sub-contracting  firm,  devised  the  following  plan  :  He  proposed 
to  enclose  the  space  to  be  occupied  by  the  tunnel  by  two  lines 
of  specially  constructed  1 2-inch  tight  sheet-piling;  upon  these 
lines  of  piling,  carefully  cut  off  at  the  proper  level,  he  would 
lay  a  timber  roof  made  of  three  layers  of  1 2-inch  timbers,  with 
courses  of  2-inch  plank  running  at  right  angles  between  the 
heavy  courses,  all  well  caulked,  and  making  a  roof  40  inches 
thick.  Under  the  protection  of  the  box  so  made,  he  proposed 
to  excavate  the  material,  either  with  or  without  the  use  of  com- 
pressed air. 

Before  driving  the  sheeting  the  river  had  been  dredged  to 
such  an  extent  as  to  leave  an  average  depth  of  7  or  8  feet  of 
material  to  be  removed  in  the  chamber  to  be  formed.  Then 
four  longitudinal  rows  of  piles  were  driven  under  the  proposed 
tunnel,  6  feet  4  inches  apart,  c.  to  c.  transversely,  and  8  feet 
apart  longitudinally.  These  piles  were  cut  off  and  capped  as 
shown  in  Fig.  64,  their  office  being  to  support  the  heavy  timber 
roof ;  to  support  the  interior  bracing  system ;  and  to  be  eventu- 
ally cut  off  at  sub-grade  and  further  support  the  finished  tunnel. 
A  substantial  pile  service  platform,  20  feet  wide,  placed  paral- 
lel to  the  tunnel  line  and  on  both  sides  of  it,  aided  materially  in 
the  accurate  alignment  of  the  bearing  piles  and  the  placing  of 
the  bracing. 

To  accurately  align  the  two  rows  of  sheet  piling,  a  timber 
frame  was  constructed  to  fit  closely  between  the  two  lines  of 


126 


MODERN    TUNNEL    PRACTICE 


io 


SUB-AQUEOUS  TUNNELS   AND  TUNNEL  SHIELDS  I2/ 

sheet  piling  to  be  driven,  with  the  center  of  this  frame  exactly 
over  the  center  line  of  the  tunnel.  This  frame,  shown  in  part 
in  Fig.  64,  was  built  in  lengths  of  216  feet,  and  floated  between 
the  service  platforms,  accurately  aligned  and  sunk.  As  this 
frame  was  now  exactly  opposite  another  frame  bolted  to  the 
pile  platform,  the  space  between  them  formed  a  true  guide  on 
either  side  for  driving  the  sheet  piling. 

The  sheet  piling  (Fig.  65)  was  made  of  12  x  1 2-inch  long- 
leaf  yellow  pine,  in  sticks  usually  65  feet  long.  Three  of  these 
sticks  were  bolted  together  so  as  to  form  a  single  unit  36  x  12 
inches;  and  these  were  "tongued  and  grooved"  by  spiking 
3  x  4-inch  pieces  on  each  edge,  suitably  arranged. 

To  further  insure  accuracy  in  the  driving  of  this  sheet  piling, 


FIG.  65. — Sheet-piling  Used  at  the  Harlem  River  Tunnel. 

pilot-piles  were  employed  with  great  advantage.  These  were 
made  of  steel  channels  and  plates,  forming  a  12  x  1 2-inch  pile 
60  feet  long.  They  were  fitted  with  pipes  running  down 
through  the  pile  point  so  that  a  water-jet  could  be  used  in 
washing  away  the  material.  Three  of  these  piles  were  very 
carefully  driven  on  the  spot  to  be  occupied  by  the  sheet  piling; 
they  were  then  withdrawn  and  the  timber  sheeting  at  once  in- 
serted in  the  hole  and  driven  to  refusal  with  a  6,ooo-pound 
hammer.  The  advantage  of  the  pilot-pile  was  that  by  its  use 
boulders  and  other  obstructions  could  be  detected  and  removed 
before  the  permanent  piling  was  driven.  The  sheeting,  when 


128  MODERN    TUNNEL    PRACTICE 

driven,  was  carefully  cut  off  by  a  circular  saw  to  the  exact 
level  required  by  the  plans. 

With  the  sheeting  in  place,  and  the  roof  described  thoroughly 
bolted  together  and  caulked,  lengths  of  this  roof,  varying  from 
39  to  130  feet  in  length,  were  floated  into  place.  Previous 
to  this  six  lines  of  12  x  1 4-inch  range  timbers  had  been  bolted 
to  the  bottom  of  this  roof ;  and  when  the  latter  was  sunk  these 
timbers  rested  exactly  upon  the  two  rows  of  sheet  piling  and 
the  four  inner  rows  of  piles.  To  the  outer  lines  of  rangers 
bolted  under  the  roof  system  T-irons  had  been  fastened,  and 
the  vertical  web  of  these  irons  cut  into  the  sheet  piling  under 
the  weight  of  the  roof.  This  T-iron  was  intended  to  assist  in 
making  a  tight  joint  between  the  roof  and  the  lines  of  the 
sheeting;  but  as  the  silt  soon  washed  in  and  closed  any  small 
crevice,  they  were  unnecessary. 

The  sunken  roof  was  next  overlaid  with  about  5  feet  of  earth 
or  mud,  dredged  from  the  immediate  vicinity,  to  bring  the  tim- 
ber roof  to  a  firm  bearing  and  also  to  provide  weight  against 
the  uplifting  tendency  of  compressed  air  used  within  the  work- 
ing chamber.  Each  end  of  this  chamber  was  closed  by  a  suit- 
able bulkhead,  making  the  length  of  the  chamber  216  feet,  or 
about  half  the  width  of  the  river.  The  other  half  of  the  river 
was  left  unobstructed  for  traffic.  In  the  center  of  this  length 
a  timber  air-shaft  was  built,  7x17  feet,  fitted  with  an  air-lock 
of  the  usual  type.  Inside  were  placed  a  rotary  and  direct- 
acting  pump  for  jetting  out  the  soft  material  excavated.  A 
material  shaft,  large  enough  to  take  in  the  segments  of  the  iron 
lining,  was  placed  near  the  center,  and  two  smaller  shafts  were 
located  between  the  center  and  the  two  ends. 

When  the  water  was  driven  from  the  working  chamber  by 
the  compressed  air,  the  leakage  of  air  from  under  the  edge  of 
the  roof  was  found  to  be  small,  considering  the  length  of  the 
sides,  and  the  sheeting  was  found  to  be  in  excellent  alignment. 
The  preliminary  work  had  evidently  been  done  with  the  great- 
est accuracy  and  care.  The  material  inside  was  excavated  with 
little  trouble,  and  the  tunnel  lined  and  concreted. 

In  building  the  shore  sections  of  the  tunnel  the  roof  was 


SUB-AQUEOUS  TUNNELS  AND  TUNNEL  SHIELDS  129 


130  MODERN    TUNNEL    PRACTICE 

omitted  altogether,  the  heavy  sheet  piling  being  considered  a 
sufficient  protection  when  suitably  braced  inside.  The  coffer- 
dam was  successfully  pumped,  and  the  space  inside  was  nearly 
completed  when  water  broke  into  the  enclosure.  It  was  found 
that  some  of  the  sheeting  had  stopped  5  to  8  feet  above  the 
rock ;  and  the  pressure  of  water  in  this  soft  material  was  suffi- 
cient to  force  its  way  under  the  sheeting.  Further  driving  of 
the  sheeting  and  the  use  of  filling,  cement,  etc.,  outside  stopped 
this  and  a  second  similar  break  that  occurred. 

For  the  building  of  the  second  half  of  the  tunnel,  Mr.  Mc- 
Bean  was  convinced  that  he  could  introduce  greater  economy 
by  substituting  the  upper  half  of  the  tunnel  itself  for  the  heavy 
timber  roof  described,  especially  as  this  timber  roof  had  no 
function  to  perform  after  the  tunnel  was  completed,  and  a  sec- 
tion of  it  actually  had  to  be  removed  later  to  provide  the  re- 
quisite depth  of  channel.  This  new  plan  was  carried  out  as 
follows : 

As  before,  the  site  was  dredged  to  nearly  sub-grade,  and  the 
double  line  of  12  x  1 2-inch  sheeting  wras  driven  for  the  sides 
and  ends  of  the  submarine  box,  with  inside  bearing  piles  and 
guide  and  bracing  frames  as  in  the  western  half.  But  the  sheet- 
ing was  now  cut  off  at  the  springing  line  of  the  proposed  tun- 
nel, instead  of  on  a  line  considerably  above  the  top  of  the  iron- 
concrete  structure  to  be  built.  The  box  thus  made  by  the  sheet- 
ing was  about  300  feet  long. 

The  roof  was  built  in  three  sections,  two  90  feet  long,  and 
one  section  84  feet  long.  To  erect  this  iron-concrete  roof  a 
floating  box  was  first  constructed,  106  feet  long,  35  feet  wide, 
and  12  feet  deep.  The  bottom  was  made  of  12  x  1 2-inch  trans- 
verse timbers  laid  4  feet  apart,  and  floored  with  3  x  1 2-inch 
planks ;  the  vertical  side  sticks  were  4x6  inches,  and  to  these 
were  spiked  3-inch  planks.  All  joints  in  the  bottom  and  sides 
were  well  caulked.  On  three  4xi2-inch  longitudinals  fas- 
tened to  the  floor  of  this  box  was  then  built  a  false  floor  for 
the  upper  half  of  the  tunnel.  This  floor  was  made  of  16  x  16- 
inch  transverse  timbers,  8  feet  apart,  and  on  these  were  placed 
a  center  longitudinal  of  10  x  1 6-inch  timber,  and  two  16  x  16- 


SUB-AQUEOUS  TUNNELS  AND  TUNNEL  SHIELDS  13! 

inch  timbers  laid  6  feet  3  inches  each  side  of  the  box-center. 
The  space  between  these  longitudinals  was  floored  with  2-inch 
plank,  spiked  to  the  16  x  1 6-inch  transverse  sticks  and  well 
caulked.  Bolts  held  this  flooring  firmly  bound  together. 
-  Upon  this  false  floor  the  cast-iron  tunnel  lining  was  erected, 
in  6- foot  rings;  and,  as  shown  in  the  illustration,  rods  and 
braces  were  introduced  as  precautions  against  any  possible  de- 
formation, and  suspension  bars  were  built  in  for  use  in  sinking 
this  roof.  The  skewbacks  are  especially  heavy,  and  have  a  wide 
horizontal  flange,  with  an  outside  vertical  guide-flange.  It 
might  be  mentioned  here  that  this  flange  was  drift-bolted  to 
the  top  of  the  sheeting  after  the  roof  was  sunk.  This  was 
done  by  leaving  openings  in  the  concrete  covering  this  flange ; 
and  the  bolts  were  then  set  by  a  diver  and  driven  by  using  a 
guide-pipe  and  a  heavy  "follower." 

To  close  the  ends  of  this  roof-box,  and  yet  to  permit  con- 
nection with  an  adjoining  section,  a  vertical  diaphragm  of  J- 
inch  iron  plate  was  so  bolted  over  the  ends  as  to  leave  a  6-foot 
shell-ring  outside  of  the  diaphragm.  In  the  center  of  the  top 
of  the  projecting  ring  was  a  specially  provided  opening  for  the 
use  of  the  diver  who  was  to  enter  this  section  and  do  the  con- 
necting of  two  main  tunnel  sections.  The  cover  was  left  off 
this  opening  until  the  diver  had  finished  his  work  inside.  Each 
6- foot  ring  of  the  iron  shell  weighed  about  41,000  pounds,  and 
it  carried  618  cubic  feet  of  concrete.  As  calculated,  the  total 
weight  of  the  iron,  concrete  floor,  etc.,  was  about  50  pounds 
less  per  lineal  foot  than  the  estimated  buoyancy  of  the  empty 
roof-chamber. 

The  concreting  having  been  completed  according  to  plan, 
the  roof  was  now  ready  to  be  lowered  down  upon  the  sheeting 
sides.  The  Bronx  shore  section,  84  feet  long,  was  the  first  to 
be  sunk.  But  before  this  was  done,  a  short  section  of  the  tun- 
nel had  been  built  in  an  open  cut  on  the  shore,  provided  with 
horizontal  air-locks,  and  presenting  a  completed  ring  for  con- 
nection, a  tight  bulkhead  having  been  built  over  it  some  little 
distance  inshore  of  the  end  before  the  end  of  the  original  cof- 
ferdam was  removed. 


132  MODERN    TUNNEL    PRACTICE 

When  all  was  ready  for  sinking,  and  suspension  tackle  had 
been  attached  to  the  eye-bars  noted  and  to  heavy  beams  rest- 
ing on  the  surface  platforms,  water  was  pumped  into  the  box 
in  which  the  roof  had  been  built  until  its  floor  sunk  below  the 
false  floor  of  the  tunnel-roof  chamber,  the  buoyancy  of  the 
latter  having  arrested  any  further  sinking  of  this  roof  portion. 
When  the  clearance  was  sufficient,  one  end  of  the  box  was  re- 
moved, and  it  was  pulled  out  lengthwise  from  under  the  roof 
portion,  and  was  used  in  building  another  roof  section.  Com- 
pressed air  was  meanwhile  pumped  into  the  roof  to  decrease 
any  leakage  through  the  false  floor  and  to  maintain  the  water 
displacement.  To  aid  in  locating  the  roof  on  the  sheeting,  fine 
wires  were  set  up  at  each  end  of  the  tunnel  section  and  aligned 
by  a  transit,  and  other  tag-lines  fastened  to  the  tunnel  roof 
were  set  for  longitudinal  and  transverse  adjustment.  With 
these  guides  the  roof  was  carefully  moved  longitudinally  until 
the  flanges  in  the  projecting  6-foot  ring  coincided  vertically 
with  the  ending  of  the  shore  section;  the  roof  was  then 
weighted  with  stone  to  overcome  its  buoyancy,  and  was  sunk 
and  connected  by  a  diver,  as  already  described.  As  showing 
the  care  taken,  the  flanges  were  bolted  together  by  i-inch  bolts 
entering  i  i-i6-inch  holes.  This  section  was  now  ready  for 
excavation,  the  separating  diaphragm  being  cut,  and  after  the 
diver  had  closed  the  opening  by  which  he  entered  the  project- 
ing ring. 

The  other  two  roof  sections  were  assembled  and  sunk  on 
the  sheeting  in  a  similar  manner;  but  the  connection  of  the 
last  section  with  the  river  end  of  the  old  western  tunnel  section 
required  some  special  provisions.  As  already  noted,  the  timber 
roof  of  this  first  section  was  placed  so  high  that  the  entire 
tunnel  section  could  be  built  under  it,  and  the  lines  of  the  sheet- 
ing were  cut  off  at  a  correspondingly  higher  level.  Under  this 
roof  a  section  of  the  tunnel,  about  47  feet  long,  was  left  un- 
built. The  problem  was  to  connect  the  lower  iron-concrete 
roof  section  with  the  high-roof  section  of  the  first,  or  western, 
half  of  the  tunnel. 

The  outside  transverse  bulkhead  of  the  high-roof  section 


SUB- AQUEOUS  TUNNELS  AND  TUNNEL  SHIELDS  133 

was  first  cut  off  to  the  level  of  the  springing  line  of  the  tunnel, 
or  to  correspond  with  the  sheeting  under  the  new  roof.  The 
river  end  of  the  last  section  of  the  new  roof  sunk  had  been 
closed  by  a  special  diaphragm,  which  had  a  flanged  base  at 
the  springing  line,  which  permitted  it  to  rest  upon  and  be  lag- 
screwed  to  the  transverse  sheeting  mentioned.  But  the  dia- 
phragm itself,  instead  of  conforming  in  shape  to  the  line  of 
the  twin-tunnel  section,  as  before,  was  now  a  rectangular  plate 


lo#  Roof  Tunnel—--  >[<—  -High  Roof  Tunnel 


Connecting 
Roof  f/afe. 


Longitudinal     Section. 

Sheeting --^.High  Side  Sheeting 

' 

a*"*" m  TJhee^ 


ENS. 
NEVVS. 


Part   Sectional     Plan    A~D. 

FIG.  67. — Manner  of  Connecting  Old  and  New  Work. 

extending  to  the  full  width  of  the  transverse  sheeting,  or  32 
feet  2  inches,  and  it  was  8  feet  4  inches  high.  To  the  top  of 
this  plate  was  connected  by  plates  and  angles  another  plate  of 
the  same  width  and  almost  5  feet  high.  In  the  lower  plate 
was  a  manhole,  20  x  30  inches,  and  angle  irons  were  riveted  to 


134  MODERN    TUNNEL    PRACTICE 

both  sides  and  the  top  of  the  diaphragm  plates,  to  receive  the 
side  plates  to  be  put  on  after  the  section  was  sunk. 

After  the  last  section  had  been  sunk  into  place  with  the  dia- 
phragm attached,  the  latter  was  first  connected  by  a  diver  to 
the  line  of  transverse  sheeting  by  lag  screws.  Then,  to  close 
a  space  of  about  14  inches  between  the  line  of  the  diaphragm 
and  the  sheeting  of  the  high-roof  section,  two  side  plates  and 
a  horizontal  roof  plate  were  lowered  into  position,  fitted  by  a 
diver  against  the  sides  and  over  the  top  of  the  roof-rangers  and 
the  bolt-holes  marked.  These  plates  were  then  taken  up,  drilled 
to  correspond  with  the  holes  in  the  diaphragm  flanges,  and  fin- 
ally bolted  to  the  timber  sides  and  roof  by  divers.  In  this  man- 
ner a  water-tight  connection  was  made  between  the  two  sec- 
tions of  the  tunnel  built  on  different  plans,  and  with  this  con- 
nection complete  the  water  was  expelled  by  compressed  air 
from  the  old  completed  tunnel,  and  the  connecting  link  of  the 
tunnel  was  built  as  in  the  original  plan.  In  the  diaphragm  as 
erected,  holes  had  been  drilled  for  the  bolts  that  were  finally 
to  connect  the  flanges  of  the  abutting  tunnel  shells,  and  other 
holes  carried  anchor-bolts  for  connecting  this  diaphragm  with 
the  concrete  backing. 

Penna.  R.  R.  Hudson  River  Tunnel — This  novel  tunnel,  for 
which  the  contract  is  let  at  this  date,  is  intended  to  connect 
Manhattan  Island,  or  New  York  City,  with  the  Pennsylvania 
Railway  System.  The  Hudson  River  section  of  the  tunnel  is 
5,502  feet  long;  though  with  its  land  terminal  connections  it 
will  be  eventually  5.7  miles  long.  Under  the  river  the  tunnel 
will  be  laid  in  two  parallel  concrete-lined  tubes,  each  supported 
on  a  row  of  27-inch  screw-piles  spaced  15  feet  apart.  The  con- 
struction shown  in  Fig.  68  is  made  necessary  by  the  unstable 
character  of  the  fine  silt  forming  the  larger  part  of  the  bed  of 
the  Hudson  River  at  New  York. 

The  cast-iron  lining,  23  feet  in  diameter,  is  of  the  usual  type, 
except  that  a  special  segment  is  inserted  at  the  point  where  the 
screw-pile  occurs.  Each  lining-ring  is  30  inches  long  and  is 
made  in  twelve  segments,  one  of  the  latter  being  a  key-segment 
12!  inches  long.  These  segments  have  flanges  n  inches  deep 


SUB-AQUEOUS  TUNNELS  AND  TUNNEL  SHIELDS  135 


Leave  Concrete  rough  as 
shown  until  Track  System 
is  ready  to  be  put  in  place, 
when  invert  of  Tunnel 
can  be  completed. 


FIG.  68.— Hudson  River  Tunnel  of  the  Pennsylvania  R.  R.  Co.:  Typical 
Section   of   One  of  the   Tubes    Supported   by    Screw-piles. 


MODERN    TUNNEL    PRACTICE 


136 

on  all  edges  of  the  segment ;  they  break  joints  longitudinally, 
and  the  key  segment  is  thus  alternately  right  and  left  of  the 
crown-line  of  the  tunnel. 


Section  KK 

FlG.  69. — Details  of  Bore-segments  of  Tube  Lining. 


SUB-AQUEOUS  TUNNELS   AND  TUNNEL  SHIELDS 


137 


The  segments  through  which  the  screw-pile  passes  are  of  spe- 
cial construction,  and  are  made  of  cast  steel,  and  in  pairs  occu- 
pying the  width  of  two  rings.  Their  construction  is  shown  in 
Fig.  69.  The  circular  opening  in  the  plates  is  intended  for  the 
shaft  of  the  screw-pile ;  and  to  permit  the  passage  of  the  bladt* 
of  the  screw  a  slot  is  left  in  the  casting,  as  shown.  A  tempo- 
rary collar  and  cast-iron  plug  close  the  hole  in  the  lining  until 
the  pile  is  put  down;  and  cast-iron  fillers  similarly  close  the 
slot  referred  to. 

The  screw-piles  are  in  general  of  the  usual  construction.  The 
helix  has  one  turn,  with  the  usual  lap,  and  a  pitch  of  21  inches. 
The  shaft  is  27  inches  in  outside  diameter  and  is  made  in  7- 
foot  lengths,  connected  by  inside  flanged  joints,  with  four 
flange  bolts  and  twelve  steel  dowels  fitting  into  adjoining  circu- 
lar mortices.  These  dowels  take  the  torsional  strains  resulting 


FIG.  70. — Detail  of  Dowel  and  Bolt  for  Screw-pile  Shaft. 

from  the  screwing-down  of  the  piles,  while  the  bolts  clamp  the 
adjoining  sections  together,  as  shown  in  Fig.  70. 

As  shown  in  the  general  cross-section,  the  upper  part  of  the 
pile  is  enclosed  in  a  sleeve.  This  is  simply  a  sheet  steel  cylinder 
placed  as  shown,  when  the  pile  has  been  driven  down  sufficiently 
to  permit  it.  Its  purpose  is  to  provide  a  sort  of  cofferdam,  in 
which  the  final  7-foot  length  of  pile  can  be  disconnected  and 
lifted  out,  and  in  which  another  pile  section  of  the  exact  re- 
quired length  can  be  inserted  and  connected  up.  The  top  12 
feet  of  the  pile  shaft  is  filled  with  concrete. 

At  or  near  the  intersection  of  grades  and  the  rock,  where 
some  distortion  may  occur  owing  to  the  difference  in  support- 


138  MODERN    TUNNEL    PRACTICE 

ing  quality  in  the  ground,  an  expansion- joint  construction  will 
be  used.  This  joint  ( Fig.  71)  will  consist  of  a  ring  within  a 
ring,  and  these  rings  will  be  made  of  wrought  steel  instead  of 
cast-iron.  The  figure  shows  a  section  through  the  rings  paral- 
lel to  the  axis  of  the  tunnel. 

Quoting  here  from  the  specifications,  we  find  that  the  tun- 
nel portion  under  the  river  is  to  be  built  by  means  of  a  shield 
and  compressed  air.  Bulkheads  and  safety  screens  are  to  be 
built  across  the  tube  at  intervals  not  exceeding  1,000  feet. 
These  bulkheads  shall  be  constructed  of  concrete,  or  brick  set 
in  Portland  cement ;  and  each  shall  have  two  air-locks  not  less 
than  6  feet  in  diameter  and  20  feet  long — one  near  the  roof,  as 
an  emergency  lock  for  the  men ;  and  one  at  the  bottom,  for  pass- 
ing material,  pipes,  rails,  etc.  An  air  pressure  of  55  pounds 


NHWS.  ''-Temporary  C.I.  Block  to  take  the. 

Reaction  of  the  Shield. 

FIG.  71. — Expansion- joint  for  Tube-tunnel  Lining. 

per  square  inch  is  to  be  provided  for  in  designing  these  bulk- 
heads. A  safety  screen,  extending  from  the  roof  downward 
into  the  tunnel,  is  to  be  maintained  within  100  feet  of  each 
working  face. 

The  contractor  is  to  design  his  own  shield,  under  certain 
specifications ;  and,  of  course,  this  cannot  be  now  described. 

Screw-jack  Shield. — In  constructing  the  water-works  at  Rip- 
ley,  N.  Y.,  Mr.  E.  A.  Wilder,  C.  E.,  devised  a  simple  shield  for 
use  in  driving  a  700- foot  tunnel  through  clay  and  a  material 
closely  approaching  quicksand. 

The  tunnel  was  circular,  42  inches  in  diameter,  lined  with 
two  rings  of  brick.  As  hydraulic  jacks  would  require  a  special 
plant  for  their  operation,  screw-jacks  were  employed  to  push 
the  shield  forward. 

This  shield  (Fig.  72)  was  made  of  f-inch  plates,  connected 
by  3  x  4-inch  angles.  As  the  circular  angle  was  cut  away  en- 


SUB-AQUEOUS  TUNNELS  AND  TUNNEL  SHIELDS 


139 


tirely  for  the  pockets  for  the  screws,  the  engineer  advises  the 
use  of  a  3  x  5  x  ^-inch  angle  for  this  purpose.  The  steel  jack- 
screws  were  i^  x  16  inches,  and  brass  nuts  were  used,  with  a 
convex  bearing  seated  on  a  thin  concave  plate  bolted  to  the  cir- 
cular flange,  but  not  rigidly.  This  arrangement  held  the  screws"" 
always  in  place,  and  at  the  same  time  permitted  a  slight  move- 
ment that  prevented  binding  of  the  screw.  The  pockets  en- 
tirely enclosing  the  screws  answered  as  brackets,  transmitting 

.-•Screw  


K  - 56" - • 

FIG.  72. — Screw-jack  Tunnel  Shield. 

the  thrust  of  the  screw  to  the  cutting  edge,  and  prevented  sand 
from  coming  in  contact  with  the  screw. 

This  shield  was  built  by  the  Erie  City  Iron  Works,  and  cost 
$140  f.  o.  b.  at  Erie,  Pa. 

Shankland  Shield — In  constructing  the  Chicago  Intercepting 
System,  in  1902-03,  a  shield  was  employed  that  was  practically 
designed  by  E.  C.  Shankland  for  the  contractor. 

This  shield  (Fig.  73)  was  24  feet  10  inches  outside  diameter, 
and  the  forward  10  feet  of  hood  was  made  of  i-inch  steel 
plates.  At  the  middle  of  this  hood  is  an  inside  ring  made  of 
two  12-inch  channels  set  back  to  back  and  12  inches  apart. 
From  the  rear  of  this  ring  a  series  of  1 2-inch  horizontal  I-beams 
are  spaced  15  inches  apart,  forming  a  series  of  chambers  for 
the  hydraulic  jacks.  The  rear  ends  of  these  I-beams  rest  upon 
another  ring  of  two  1 2-inch  channels.  The  front  part  of  the 


I4O  MODERN    TUNNEL    PRACTICE 

hood  is  stiffened  by  eight  deep  gusset  plates,  forming  exten- 
sions of  the  central,  vertical  and  three  horizontal  partitions. 
At  the  intermediate  points  there  are  shallower  gusset  plates; 
and  all  these  plates  are  riveted  to  horizontal  steel  angles  inside 
the  shell,  and  to  other  angles  against  the  1 2-inch  channel  ring. 
The  partitions,  dividing  the  shell  into  sixteen  compartments, 
are  made  of  f-inch  steel  plate,  stiffened  by  double  rows  of  12- 
inch  steel  channels. 

The  shield  was  fitted  with  thirty  65-ton  hydraulic  jacks,  the 
5-inch  plunger  of  each  jack  having  an  end  bearing  plate,  8  x  26 


4b 


°Skw,. 


{"Steel 


KM 


K'1,401^ 


Half  Rear  Elevation. 


Half  Front  Elevation. 


Longitudinal       Section. 


FIG.  73.— Chicago  Sewer  Tunnel :  The  Shankland  Shield. 

inches,  butted  against  the  8-inch  circular  wooden  tunnel  lining 
projecting  into  the  tail  of  the  shield.  The  brickwork  is  built 
inside  this  lining,  the  latter  being  left  in  place.  The  average 
rate  of  progress  with  this  shield,  in  93  days,  was  8.74  feet  of 
tunnel  in  24  hours. 

Timber-lined  Subaqueous  Tunnel — In  1901  the  Massachusetts 
Pipe  Line  Gas  Company  was  compelled  to  carry  its  pipe  system 
under  the  Mystic  and  Charles  rivers,  near  Boston.  Subaqueous 
tunnel  siphons  were  built  for  this  purpose ;  and  the  42  and  54- 


SUB-AQUEOUS  TUNNELS  AND  TUNNEL  SHIELDS 


141 


inch  cast-iron  pipes  were  protected  against  corrosion  by  con- 
creting them  inside  a  wood-lined  shaft  and  tunnel,  as  here 
described. 

The  shafts  were  sunk  by  using  an  ordinary  air-lock  sur- 
mounting a  riveted  steel  caisson.  This  caisson  was  sunk  in  the_ 
usual  way  and  extended  in  lo-foot  sections,  until  material  was 
reached  sufficiently  compact  to  prevent  the  escape  of  air.  The 
steel  caisson  was  then  stopped,  and  a  segmental  plank  lining 
was  put  in.  This  lagging  consisted  of  circular  segments  6 
inches  wide,  sawed  from  2-inch  plank,  and  the  circle  had  an 
outer  diameter  of  7  feet.  There  were  eight  segments  to  a  ring, 


Detail     of    Cutting     Edg< 

FIG.  74.— Details  of  Shankland  Shield. 

and  these  were  spiked  together  with  7-inch  spikes,  each  ring 
breaking  joint  with  the  one  below  it.  This  construction  was 
found  to  be  exceedingly  rigid,  and  it  was  used  in  building  the 
tunnel  proper.  The  curved  connection  between  the  shaft  and 
the  tunnel  was  made  by  successively  lengthening  the  diameter 
of  each  ring  in  the  direction  of  the  axis  of  the  tunnel,  as  shown 
in  Fig.  743. 

In  driving  the  tunnels  a  simple  shield  of  the  Greathead  type 
was  employed.     The  excavation  was  carried  two  feet  ahead  of 


142 


MODERN    TUNNEL    PRACTICE 


this  shield  by  placing  boards  and  posts ;  and  the  shield  was 
then  pushed  forward  by  six  hydraulic  jacks  abutting  directly 
against  the  wood  lining.  This  operation  also  tended  to  close 
up  the  joints  in  the  lagging;  though,  as  the  timber  was  thor- 
oughly dry  when  put  in,  the  swelling  of  this  timber  usually 


f    £•;    '.  i-7.--, ~«-T.,V-  /TvJA 
ft^g-*»-v.^>--.-ft**fti« 

PIG.  74a. — Charlestown    Siphon    Tunnel :    Showing    Method    of    Grouting 

Cast-iron  Pipe. 

made  very  tight  work.  The  lining  was  given  a  wash  of  thin 
cement  after  it  was  in  place ;  and  any  special  leaks  were  plugged 
by  wooden  wedges  and  caulked,  or  dry  cement  was  fed  into  the 
holes  and  carried  outward  by  the  air  pressure. 

To  preserve  the  cast-iron  pipes  from  corrosion,  and  espe- 
cially to  avoid  any  opportunity  for  gas-pockets  due  to  leakage, 


SUB-AQUEOUS  TUNNELS  AND  TUNNEL  SHIELDS  143 

the  space  between  the  pipes  and  the  wooden  lining  was  filled 
with  concrete  where  space  permitted,  or  with  injected  grout. 
In  the  latter  case  the  grout  was  run  in  pipes  to  holes  drilled  in 
the  top  of  each  length  of  cast-iron  pipe ;  and,  after  various  de- 
vices had  been  tried  and  abandoned,  owing  to  clogging,  the 
pressure  due  to  the  height  of  the  mixing  trough  at  the  surface 
was  alone  used.  But  the  grout  pipe  leading  through  the  large 
gas  pipe  was  washed  out  with  clean  water  after  every  run. 

The  cost  of  this  work  is  given  for  the  several  tunnels  as 
follows:*  The  Maiden  tunnel,  here  illustrated,  cost  $55.64  per 


Alter  i 


End  Elevation.  Section  A~B. 

FIG.  74b. — Shield  Used  by  Massachusetts  Pipe  Line  Gas  Co. 

lineal  foot  complete;  or  $35.34  per  foot  for  driving  the  tunnel, 
$15.50  per  foot  for  the  54-inch  pipe,  and  $4.80  per  foot  for 
laying  and  grouting.  The  Charleston  tunnel  was  built  without 
a  shield,  but  under  air  pressure.  The  total  cost  was  $101.40 
per  lineal  foot;  or,  driving  $87.45,  42-inch  pipe  $4.35  per  foot, 
laying  and  concreting  $9.60  per  foot.  The  River  Street  tunnel 
was  90  feet  below  the  water  level ;  it  was  also  built  without  a 
shield  and  under  great  difficulties.  It  cost  $99.65  per  lineal 
foot;  or,  driving  $/i8.8/t  per  foot,  48-inch  pipe  $5.36  per  foot, 
laying  and  concreting  $45.45  per  foot.  The  cost  of  labor  on 
the  concrete  was  about  $5  per  cubic  yard ;  and  the  concrete 
complete  in  the  tunnel  cost  about  $9  per  cubic  yard. 
^Engineering  News,  Oct.  3,  1901 ;  p.  229. 


CHAPTER    VIII 

SUBWAYS,    OR    UNDERGROUND    RAILWAYS 

Location  of— Orleans  Railway  in  Paris— Metropolitan  Railway  of  Paris- 
Boston  Subway— East  Boston  tunnel— Buda-Pest  Subway— New  York 
Rapid  Transit  Subway — Atlantic  Avenue  Subway  in  Brooklyn. 

Subways,  or  railways  of  this  type,  are  comparatively  very 
modern  in  their  application.  They  have  for  their  object  the 
shortening  of  time  of  transit  between  given  points  in  a  great 
city,  and  the  relief  of  the  surface  streets  from  congestion  of 
traffic. 

Subways  are  constructed  both  in  tunnels  and  in  open  cuts; 
and  they  may  be  combined  with  the  elevated  roads  where  the 
conditions  demand  such  a  combination.  The  extensions  of 
these  subways  may  be  carried  under  rivers  separating  parts  of 
a  great  city;  but  in  such  cases  these  extensions  are  properly 
classed  as  subaqueous  tunnels,  and  they  are  here  treated  under 
that  head. 

Subways  are  usually  located  as  near  to  the  general  street 
surface  as  conditions  will  warrant,  for  the  convenience  of  the 
people  using  them,  or  to  avoid  as  much  as  possible  the  use  of 
long  flights  of  stairs,  or  elevators,  at  the  stations.  At  the 
same  time,  provision  must  be  made  in  this  location  and  con- 
struction for  all  existing  sewers,  water  and  gas  mains,  electrical 
conduits,  and  other  underground  pipe  or  conduit  systems.  The 
sewers  and  water  and  gas  mains  are  usually  carried  over  the 
subway;  and  wire  conduits  are  provided  for  in  the  construc- 
tion of  the  abutment  walls. 

Tunneling  close  to  the  street  surface  involves  open-cut  work, 
with  all  its  obstruction  to  street  traffic;  or  the  use  of  some 
form  of  roof-shield,  when  the  soil  conditions  and  the  depth 

144 


SUBWAYS,    OR    UNDERGROUND    RAILWAYS  145 

of  the  covering  will  permit.     In  solid  rock,  and  at  a  sufficient 
depth,  the  usual  method  of  rock-tunneling  is  resorted  to. 

In  some  of  the  original  London  subways,  driven  through 
a  practically  homogeneous  clay  formation,  the  tunnels  are  cir- 
cular in  section,  with  one  tunnel  devoted  to  each  of  the  two - 
tracks.  The  advantages  claimed  by  the  advocates  of  this  twin- 
tunnel  system  are:  That  this  arrangement  results  in  a  lower 
initial  cost,  as  the  section  of  the  separate  tunnels  is  less  than 
that  of  a  double-track  tunnel ;  and,  as  these  separate  tunnels 
can  be  arranged  side  by  side,  or  one  over  the  other,  the  double 
line  can  be  kept  below  a  comparatively  narrow  street.  There, 
are  also  advantages  in  the  ventilation  of  a  single  tunnel,  by 
means  of  the  continuous  passage  of  trains  in  one  direction ;  and 
the  possibility  of  collision  in  meeting  trains  is  eliminated. 

But  there  are  also  objections  to  this  twin-tunnel  plan,  espe- 
cially from  the  point  of  view  of  operation;  and  the  cost  of 
maintenance  of  way  is  relatively  increased,  as  is  that  of  in- 
spection and  signaling.  The  stations  on  the  twin-tunnel  sys- 
tem cost  more,  as  they  are  necessarily  more  complicated  in  the 
arrangements  for  entrance  and  exit.  The  inability  to  switch 
over  from  one  line  to  another  is  also  objectionable,  and  special 
cross-overs  must  be  provided. 

Orleans  Railway  Tunnel  in  Paris — This  extension  of  the  Or- 
leans railway  system  into  the  heart  of  Paris  comes  properly 
under  the  head  of  subways  in  the  method  of  its  construction. 
The  execution  of  the  work  presented  exceptional  difficulties : 
The  extrados  of  the  arch  was  very  near  the  street  surface, 
while  the  foundation  was  at  times  below  the  water  level;  the 
alignment  was  a  succession  of  curves  of  large  radius;  many 
sewers  were  cut ;  and  the  abutments  of  bridges,  quay  walls,  old 
masonry  and  other  obstructions  were  constantly  encountered. 
The  soil  itself  was  made  up  of  the  rubbish  of  many  epochs; 
and  the  contract  demanded  that  traffic  should  not  be  interrupted 
on  the  streets  above. 

The  standard  section,  inside  the  masonry  arch  and  side  walls, 
is  as  follows :  Span  at  springing  line,  29.52  feet ;  level  of  rail  to 
springing  line,  6  feet;  rise  of  arch,  10.38  feet.  The  side  walls 


146  MODERN    TUNNEL    PRACTICE 

are  2.62  feet  thick  throughout,  and  the  arch  is  2  feet  thick  at 
the  crown,  increasing  to  2.62  feet  at  the  spring. 

The  conditions  noted,  and  especially  the  unreliable  character 
of  the  soil,  necessitated  the  shield  method  of  execution.  The 
plan  of  attack  adopted  was  to  drive  the  side  galleries,  and  in 
these  timbered  galleries  to  erect  the  masonry  side  walls  as  a 
support  for  the  roof-shield  to  be  used  in  excavating  the  remain- 
ing section.  These  side  galleries  were  6.6  feet  wide  at  the  top, 
and  this  top  extended  2.3  feet  above  the  springing  line  of  the 
arch. 

The  roof-shield  was  practically  the  same  in  design  as  the 
one  previously  used  so  successfully  at  Clichy,  in  Paris.  But  in 
this  case  the  shield  was  guided  around  the  numerous  curves  by 
lateral  rollers ;  and  an  important  modification  was  made  in  the 
method  of  sustaining  the  soil  behind  the  shield. 

As  shown  in  Fig.  75,  the  shield  included  a  steel  skin  A, 
made  of  two  plates  each  f  inch  thick.  This  skin  was  supported 
by  a  double-latticed  truss,  with  the  ten  hydraulic  jacks  located 
in  the  lower  truss.  It  was  provided  with  the  usual  front  hood, 
cut  away  at  an  angle  of  about  45°.  The  latticed  beam  H  tied 
the  trusses  together  and  formed  the  floor  of  the  shield.  As 
compressed  air  was  not  used,  the  shield  was  not  fitted  with 
a  transverse  bulkhead. 

To  guide  the  shield  laterally  in  its  forward  motion,  side 
rollers  were  provided,  running  upon  planks  of  hardwood  cov- 
ered with  steel  plates,  and  attached  to  the  masonry  inside  the 
side  walls.  These  are  shown  in  Fig.  75. 

The  method  of  sustaining  the  earth  behind  the  shield  was 
novel.  Upon  special  latticed  centering  trusses  provided,  and 
held  up  by  posts  and  braces  leading  to  the  center  core  of  soil, 
latticed  beams  e  (Fig.  76)  were  placed  longitudinally  and 
held  in  place  by  angle  irons  on  the  centering  trusses.  These 
longitudinal  beams  carried  a  series  of  small  hydraulic  presses 
u,  with  the  upper  end  of  the  press  buried  in  a  timber  /  (Fig. 
75b),  which  was  about  8  inches  thick  and  sheeted  with  steel 
plate  on  the  soil  side.  These  beams  e  were  of  different 
lengths,  corresponding  to  the  stage  of  construction  in  the  arch 


SUBWAYS,    OR    UNDERGROUND   RAILWAYS 

I 


148  MODERN    TUNNEL    PRACTICE 

masonry — the  longest,  26.24  feet,  being  at  the  key;  and  the 
shortest,  9.84  feet,  at  the  springing  line.  Small  screws  g 
running  in  the  space  between  the  latticed  shield  trusses  were 
used  in.  separately  pulling  forward  the  latticed  beams  e  and 
the  8-inch  timbers  /  attached  to  them,  the  beams  slipping  in 
the  angle-iron  guides.  The  greatest  difficulty  in  using  this 
method  lay  in  the  great  friction  encountered  in  hauling  these 
members  forward ;  but  the  French  engineer  believed,  neverthe- 
less, that  this  system  possessed  important  advantages 
over  the  old  method  of  building  the  masonry  under  a 
rear  shield,  as  all  necessary  openings  in  the  arch  work  are 
made  easily. 

The  ten  hydraulic  jacks  used  in  forcing  the  shield  forward 
exerted  a  combined  force  of  1,000  metric  tons.  These  jacks, 
instead  of  reacting  upon  the  finished  masonry,  as  usual,  abutted 
against  solid  continuing  struts  passing  through  the  centering 
system,  as  shown  at  h  (Fig.  76). 

In  operating  this  roof  shield,  the  shield  was  first  advanced 
its  length  by  the  push  of  the  jacks;  the  shield  rolling  on  the 
rollers  b  placed  under  the  beam  C  at  the  base  of  the  shield. 
The  sills  and  wedges  are  then  laid  for  the  new  center  which  is 
erected  to  take  the  place  vacated  by  the  shield.  The  beams  e 
and  the  8-inch  timbers  f  are  pulled  forward  as  the  masonry 
advances;  the  small  hydraulic  presses  u  being  operated  to 
push  up  the  timbers  /  into  the  space  left  by  the  advancing 
shield. 

The  arch  masonry  is  built  up  at  the  haunches  on  small  steel 
forms,  and  is  continued  on  lagging  held  up  by  the  same  cen- 
tering truss  that  holds  the  longitudinal  beams  e.  The  arch 
was  constructed  of  beton  blocks,  molded  and  thoroughly  set 
before  they  were  brought  to  the  work.  Masonry  was  laid  con- 
tinuously, day  and  night. 

Roof -shield  of  the  Paris  Metropolitan  Railway This  shield  is 

interesting  as  embodying  the  latest  practice  of  the  French  engi- 
neers in  shield  construction.  The  roof  of  the  Metropolitan 
Railway  of  Paris  is  but  little  below  the  surface  of  the  street; 
and  the  tunnel  is  a  double-track  structure  with  a  clear  span  of 


SUBWAYS,    OR    UNDERGROUND    RAILWAYS 


P4 


149 


b 


II 


bfi 
C 

o 

JZ 

in 


150  MODERN    TUNNEL    PRACTICE 

23.29  feet  and  a  rise  of  6.79  feet  in  the  arch.    The  arch,  abut- 
ments and  floor  are  all  in  masonry. 

The  first,  or  Vincennes-Maillot  portion  of  this  railway 
was  partly  constructed  in  1898  by  means  of  a  modification  of 
the  Clichy  sewer  shield,  previously  here  described.  This  was  a 
half-section  shield,  on  which  the  arch  was  built  and  the  abut- 
ments constructed  last,  though  in  some  cases  the  abutments 
were  built  in  advance  and  the  shield  pushed  forward  on  them. 
But  the  results  were  not  satisfactory  on  the  Metropolitan  line, 
and  much  of  the  work  was  really  done  by  ordinary  methods  of 
timbering.  The  failure  of  the  shield  was  largely  due  to  the 
fact  that  the  soil  penetrated  was  not  homogeneous,  being  largely 
filled  ground,  with  old  foundation  walls  and  broken  masses  of 
masonry  interspersed  through  it.  Then,  too,  in  moving  for- 
ward, the  shield  carried  with  it,  around  its  outer  surface,  a  cer- 
tain thickness  of  earth  which  caused  undulations  in  the  surface 
ground,  and  by  its  broken  condition  threw  too  much  weight  on 
the  tail-end  of  the  shield.  There  was  thus  a  tendency  in  the 
shield  to  rise  at  the  forward  end,  while  the  fresh  arch  masonry 
was  damaged  under  the  friction  of  the  shield  when  this  was 
moved  forward. 

The  shield  here  shown  was  devised  by  the  engineers,  Radenac 
and  Raguet,  especially  to  avoid  these  troubles,  and  in  actual  use 
it  has  been  advanced  as  much  as  20  feet  in  24  hours'  work. 

The  characteristic  features  of  this  new  roof-shield  are :  Its 
length  and  the  more  stable  support  provided  for  the  shield-roll- 
ers when  the  shield  is  moved  forward.  Instead  of  operating  the 
rollers  on  top  of  freshly  laid  masonry,  as  is  often  done,  the  steel 
centers  here  employed  are  firmly  braced  together,  and  they  are 
so  supported  and  tied  together  at  the  bottom  that  they  are  prac- 
tically immovable.  As  these  centers  carry  the  tracks  on  which 
the  shield  moves  forward,  this  forward  movement  is  steady  and 
the  surface  settlements  or  undulations  do  not  exceed  three 
inches. 

The  shield  is  made  of  an  outer  sheet-steel  shell,  ismm.  thick 
and  shaped  to  the  extrados  of  the  arch,  and  the  total  length  of 
this  shell  is  7. 5m.  (24.6  feet).  The  shell  is  supported  by  four 


SUBWAYS,    OR    UNDERGROUND    RAILWAYS 


152  MODERN    TUNNEL    PRACTICE 

cross-beams  shaped  to  the  shell  and  connected  by  38  longitudi- 
nal girders,  of  which  20  extend  forward  to  support  the  forward 
end,  and  14  carry  the  rear  end.  As  arranged  the  bottom  of  the 
shell  is  o.68m.  (2.23  feet)  above  the  springing  line  of  the  tun- 
nel and  the  forward  end  of  the  shell  is  shaped  like  a  hood  with 
four  set-backs  of  about  one  foot  each  on  each  side  of  the  axis. 
The  shell  is  fastened  to  the  girders  by  countersunk  bolts,  pre- 
senting a  smooth  surface  outside.  The  webs  of  the  girders  are 
stiffened  with  angle-iron,  making  a  box-beam  of  each  pair  of 
girders,  or  19  in  all.  Ten  of  these  box-beams  support  the  rollers, 
and  the  9  beams  coming  between  them  carry  the  hydraulic 
jacks.  All  of  the  members  of  this  shield  are  connected  by  bolts 
in  such  manner  that  it  can  be  readily  taken  apart  after  use,  and 
the  total  weight  of  the  shell  and  its  framework  is  67,540 
pounds.  The  cast-steel  cutters  on  the  front  of  the  hood  are 
8  in  number,  each  about  3^  inches  thick  by  6  inches  wide,  and 
these  are  bolted  to  the  shield  by  f-inch  bolts. 

The  centers  upon  which  the  rollers  operate  are  built  beams 
shaped  to  the  arch  and  divided  into  two  equal  parts  connected 
by  means  of  bolts.  The  foot  of  this  center  extends  about  18 
inches  below  the  spring  of  the  arch,  and  it  there  rests  upon  a 
cross-tie  made  of  two  steel  plates  and  angles.  This  tie  is  put  in 
to  obviate  a  tendency  in  the  center  to  spread,  and  the  whole 
center  is  carried  on  longitudinal  sills  supported  by  posts  driven 
into  the  undisturbed  ground  of  the  lower  advance  gallery. 

There  are  usually  30  of  these  centers  under  the  shield  and 
the  finished  masonry  at  one  time;  each  center  weighs  about 
1,980  Ibs.,  and  they  are  spaced  one  metre  (3.28  feet)  apart,  c. 
to  c.  On  top  of  this  series  of  centers  there  is  a  projection 
in  the  axis  of  each  of  the  19  box-beams  carried  by  these 
centers,  and  each  center  is  connected  to  its  mate  by  a  series 
of  cast-iron  beams  fitted  with  shoes  and  bolt-holes.  The  top 
of  each  of  these  connecting  beams  carries  a  rail  2.56  inches 
high,  which  is  also  the  depth  of  the  lagging  to  be  used  in  lay- 
ing the  masonry  on  these  centers.  Arrangement  is  also  made 
on  these  connecting  beams  for  attaching  the  thrust-blocks  of 
the  hydraulic  jacks. 


SUBWAYS,    OR    UNDERGROUND    RAILWAYS  153 

The  rollers  are  attached  to  the  framework  of  the  shell,  and 
are  set  in  10  rows;  the  6  rows  in  the  middle  having  6  rollers 
each,  and  the  2  rows  on  each  side  having  5  rollers.  These 
rollers  are  made  of  cast-iron,  double-flanged  to  prevent  them 
running  off  the  tracks,  and  with  an  extra  width  between  the 
flanges  so  as  to  permit  the  guiding  of  the  shield  in  its  forward 
movement.  Each  roller  is  mounted  on  a  3! -inch  soft-steel  axle, 
16.34  inches  long,  supported  in  castings  bolted  to  the  frame. 

The  hydraulic  jacks  are  each  8.8  feet  long  over  all,  and  they 
have  a  stroke  of  3.7  feet.  While  place  was  made  for  9  hy- 
draulic jacks,  only  7  were  actually  installed,  and  4  do  all  the 
work  required.  Each  jack  exerts  a  maximum  pressure  of  50 
tons. 

In  operating  this  shield  a  bottom  gallery  is  first  pushed 
forward,  and  into  this  gallery  is  thrown  the  material  exca- 
vated at  the  front  of  the  shield.  Before  the  shield  is  advanced, 
a  new  center-rib  is  set  up  and  securely  bolted  to  its  predeces- 
sors, the  roller-track  for  the  shield  being  also  lengthened  by 
the  span  of  the  new  center,  or  by  one  meter.  The  hydraulic 
jacks  are  fastened  to  the  shell  framework,  and  the  pistons  of 
the  jacks  act  upon  thrust-blocks  set  between  the  center-ribs. 
As  these  ribs  are  theoretically  immovable,  the  shield-shell  and 
its  framework  advance.  As  the  shield  moves  forward,  sheets 
of  thin  steel  replace  it  and  prevent  the  earth  from  falling  in, 
and  these  plates  are  held  in  place  by  temporary  timbering  until 
the  masonry  is  completed,  the  plates  remaining  in  the  ground. 

The  masonry  is  thus  actually  built  behind  the  shield  and  not 
under  it.  The  rear  of  the  shield  is  shaped  with  two  off-sets  on 
each  side,  and  the  arch  masonry  is  thus  being  laid  with  the 
abutment  portions  continually  in  advance  of  the  crown  of  the 
arch.  The  masonry  is  built  on  wooden  lagging  laid  upon  the 
steel  centers,  and  it  completely  fills  the  space  between  this 
lagging  and  the  steel  top-plates,  the  temporary  props  under 
these  plates  being  removed  as  far  as  possible. 

The  crew  for  this  shield  work  was  made  up  as  follows :  One 
foreman  and  one  machinist;  4  carpenters  and  i  helper,  to 
take  down  and  put  up  centers ;  4  miners,  working  at  the  face ; 


154  MODERN    TUNNEL    PRACTICE 

8  laborers,  6  shoveling  and  2  attending  to  cars  in  the  advance, 
lower  gallery.  In  addition  to  these,  5  masons  and  5  helpers 
were  at  work  on  the  masonry ;  the  masons  working  on  the  low 
wall  that  lies  under  the  shield  and  along  the  springing-line  on 
both  sides  in  the  intervals  between  advances  of  the  shield. 
With  the  arch  masonry  complete,  the  two  side  walls  and  the 
floor  of  the  tunnel  are  built  by  underpinning  the  arch  as  the 
bottom  material  is  excavated. 

Boston  Subway  System — Boston,  a  few  years  ago,  had  proba- 
bly a  more  complicated  and  congested  electric  street-railway 
system  than  any  other  in  the  United  States,  and  these  condi- 
tions resulted  in  Boston  being  the  first  of  our  cities  to  construct 
a  regular  system  of  underground  lines  for  its  electric  street- 
railway  service. 

Without  entering  intq^the  detail  of  routes,  it  is  sufficient  to 
say  the  plan  adopted  by  the  Boston  Rapid  Transit  Commission 
of  1895  contemplated  the  construction  of  about  5,600  feet  of 
double-track  subways,  and  about  3,500  feet  of  four-track  sub- 
ways. These  subways  were  to  be  ventilated  by  fans  driven  by 
electric  motors,  and  well  lighted  by  electric  lights.  The  chief 
engineer  was  Mr.  Howard  A.  Carson,  M.  Am.  Soc.  C.  E. 

The  material  to  be  penetrated  was  mainly  earth,  sand  and 
gravel,  and  the  conditions  were  generally  favorable,  the  maxi- 
mum depth  of  excavation  being  38  feet.  The  grades  were  3% 
and  5%,  and  changes  in  direction,  were  made  by  curves  of 
700-foot  radius  on  the  center  line. 

As  shown  in  Fig.  77,  the  general  construction  consisted  of  a 
concrete  invert,  side  walls  of  steel  columns  with  concrete  filled 
between,  and  a  roof  of  plate-girders  or  I-beams,  with  brick 
jack-arches  between  them,  the  whole  covered  by  concrete.  In 
the  four-track  lines  a  middle  column  supported  the  roof.  The 
detailed  dimensions  are  given  in  the  illustration.  The  steel 
columns  were  spaced  6  feet  apart,  with  a  V-brace  of  3  x  f -inch 
angle-iron  in  each  panel  and  a  longitudinal  tie  at  the  base  of  the 
post  made  of  a  similar  angle. 

One  of  the  ventilating  chambers  is  shown  in  Fig.  78.  It  is  a 
concrete  chamber  fitted  with  a  ventilating  fan  driven  by  an 


SUBWAYS,    OR    UNDERGROUND    RAILWAYS 


155 


.    . 


uoiuuoy  sfuuHQj.  »pis 


156  MODERN    TUNNEL    PRACTICE 

electric  motor,  the  air  exhausted  being  discharged  through  an 
air-duct  6^  feet  in  diameter. 

This  subway  was  largely  built  in  open  cut,  and  this  portion 
of  the  work  requires  no  special  explanation. 

About  one-third  of  the  length  of  this  subway  is  tunnel, 
with  a  concrete  invert,  side  walls  and  haunching,  and  a  brick 
arch,  as  shown  in  Fig.  79.  The  peculiar  feature  of  this  system 
of  construction  is  the  use  of  the  tie-rods  through  the  crown  of 
the  arch,  intended  to  prevent  any  deformation  of  the  arch  due 


Section  F-F 


FIG.  78. — Boston  Subway :  Ventilating  Chamber. 


to  eccentric  loading,  as  the  street  surface  is  very  near  at  some 
points. 

In  tunneling,  the  two  side  walls  were  built  in  advanced  head- 
ings ;  the  arch  was  then  built  by  means  of  a  shield  supported  on 
the  side  walls,  and  the  center  core  of  material  was  removed 
later.  The  concrete  side  walls  are  double.  The  outer  wall,  6 
to  12  inches  thick,  is  backed  directly  against  the  sides  of  the  ex- 
cavation, and  the  inner  face  is  then  plastered  with  an  asphalt 
composition  to  make  it  watertight. 


SUBWAYS,    OR    UNDERGROUND    RAILWAYS 


157 


For  the  tunnel  section  a  roof-shield  was  employed  of  the  type 
here  shown.  The  position  of  the  shield  in  relation  to  the  tunnel 
section  is  shown  in  Fig1.  80.  The  shield  weighed  about  22 
tons  and  cost  about  $6,000.  It  was  calculated  to  sustain  an 
approximate  load  of  640,000  pounds.  It  was  29  feet  4  inches 
wide  over  all,  and  had  a  rise  of  4  feet  45-16  inches.  The  shield 
is  composed  of  two  plate-girders  3  feet  8  inches  deep  and  4  feet 
apart,  with  cover  plates  extending  4  feet  beyond  the  girder, 
while  an  additional  top-plate  extends  2  feet  to  the  rear.  Under 
each  foot  of  each  girder  is  an  iron  casting  with  a  spherical  pro- 
jection on  the  under  side,  which  fits  into  a  recess  in  a  cast-steel 
shoe,  the  surface  in  contact  being  planed  to  a  truly  spherical 


FIG.   79. — Typical  Section  of  the  Boston  Subway,   in  Concrete  and  Brick 
Work ;  Double-track. 

surface.  These  shoes  rest  upon  two  lines  of  lo-inch  steel 
I-beams  imbedded  in  the  tops  of  the  concrete  side  walls,  form- 
ing a  track  upon  which  the  roof-shield  slides  as  it  is  pushed 
forward. 

The  girders  are  divided  into  10  panels  by  transverse  f-inch 
webs,  and  a  6-inch  hydraulic  jack  is  located  between  the  girders 
in  each  panel.  The  closed  ends  of  these  jacks  are  supported  by 
the  castings  shown  in  the  figure.  The  6-inch  plungers  of  the 
jacks  pass  through  loj-inch  holes  in  the  web  of  the  rear  girder, 
the  outer  ends  of  the  plungers  being  fitted  with  collars,  which 
latter  abut  upon  2^-inch  cast-iron  round  bars,  about  2  feet  10 


158  MODERN    TUNNEL    PRACTICE 

inches  long,  with  2|-inch  pipe-sleeves  at  the  joints.  These  iron 
bars  are  built  into  the  brickwork  of  the  arch  and  form  continu- 
ous lines  of  metal  to  resist  the  thrust  of  the  jacks ;  a  device  ap- 
parently first  used  by  Mr.  Walton  I.  Aims  in  the  East  River 
gas  tunnel,  at  New  York. 

In  moving  the  shield  forward  the  pipes  leading  to  the  jacks 
are  brought  under  the  rear  of  the  shield,  and  they  are  fitted 
with  valves,  so  that  a  man  at  this  point  can  direct  and  regulate 
the  direction  of  the  advance  by  varying  the  pressure  on  each 
jack;  men  stationed  at  each  jack  watching  and  measuring  the 


Details  of  Casting 
Supporting  Ends  of  Jar 


Details  of  Casting  under  Ends 
of  Girders. 


Longitudinal    Section  C-Q. 

FIG.  80. — Detail  of  Roof-shield,  Boston  Subway. 


advance  simultaneously.  As  soon  as  the  shield  has  been  pushed 
forward  about  3  feet  the  timber  centering  is  erected  behind  it 
and  the  brick  arch  is  built. 

During  this  time  a  heading  6  feet  high  and  the  whole  width 
of  the  tunnel  is  excavated  ahead  of  the  shield  and  supported  by 
posts  and  poling-boards,  which  are  removed  as  the  shield 
reaches  them.  In  the  subway  work  in  Boston  the  material  was 
mainly  gravel  and  stiff  clay ;  the  depth  of  earth  above  the  tunnel 


SUBWAYS,    OR    UNDERGROUND    RAILWAYS 


159 


roof  varying  from  6  feet  9  inches  to  13  feet.     A  progress  of 
about  50  feet  per  week  was  made. 

East  Boston  Tunnel — The  construction  of  the  Atlantic  Ave- 
nue station  of  the  Boston  Subway  Extension,  to  East  Boston, 
furnishes  an  interesting  example  of  wide-arch,  soft-ground  tun- 
neling. As  shown  in  Fig.  82,  this  station  is  deep  under  ground 
and  below  the  water-level,  and  at  each  end  it  connects  with  a 
standard  double-track  tunnel  which  is  23  feet  8  inches  wide  by 
20  feet  8  inches  high.  The  entrance  shaft  to  the  station  is 


Surfact  of  Strut.                                                                                              , 

r^T'^ 

4.Qa9   '  '                                            f.T.C.Ct                  Q      QlS'Stwtr 

HgW* 

if 

n 

g;|»»~ 

0           5-         »'                     20' 

T 

>i 

1 
5 

R 

FIG.  82. — East  Boston  Tunnel ;  Atlantic  Avenue  Station. 

40  x  57^  feet  in  plan,  and  will  contain  elevators,  stairways,  etc., 
and  this  was  built  by  sinking  pits  from  the  surface.  The  station 
portion  proper  is  150  feet  long. 

This  station  tunnel  comes  entirely  within  a  blueTclay  stra- 
tum, with  occasional  pockets  of  sandy  clay.  The  side  walls 
were  built  first,  as  shown  in  Fig.  83.  A  bottom  drift  was  first 
opened  and  timbered  as  at  a;  the  side  boarding  was  then 
replaced  by  a  lagging  of  corrugated  boards,  and  behind  this 
was  built  a  6-inch  concrete  wall,  as  shown  at  b.  A  portion 


i6o 


MODERN    TUNNEL    PRACTICE 


of  the  side  wall  and  invert  were  then  laid,  as  in  b  and  c; 
and  a  second  drift  was  started  above  the  first  and  timbered,  as 
shown  by  e,  and  in  this  drift  the  6-inch  concrete  wall  was 
carried  up  as  before;  the  side  wall  was  next  carried  up,  as 
at  /.  This  operation  completes  the  wall  to  the  springing  line  of 
the  arch,  both  side  walls  being  constructed  simultaneously.  It 
is  understood  that  this  side-wall  work  is  a  continuous  operation. 
And  it  will  be  noted  that  the  bottom  drift — at  track  level — has 
a  spoil-car  platform. 

The  construction  of  the  roof-arch  follows  close  behind  the 


FIG.  83. — Sequence  of  Operations  in  Building  the  Side-walls  at  the  Atlantic 

Avenue  Station. 

completed  side  walls,  and  the  method  of  procedure  is  shown  in 
Fig.  84.  A  crown  heading  A,  8  feet  wide  and  ?J  feet  high,  is 
driven  and  timbered,  and  over  the  caps  are  inserted  four  sheet- 
steel  poling-boards.  Ahead  of  A  and  below  it,  is  driven  a  sec- 
ond heading  B,  8  x  6  feet ;  this  latter  heading  serves  for  the 
removal  of  the  soil.  From  heading  A  a  drift  is  carried  right 


SUBWAYS,    OR    UNDERGROUND    RAILWAYS 


161 


and  left  toward  the  haunches,  steel  poling-boards  being-  inserted 
and  braced  by  radial  struts  from  the  core  below.  On  each 
haunch  and  at  the  same  time  the  drifts  D  are  driven  and  roofed 
in  a  similar  manner,  working  toward  the  springing  lines.  When 
drifts  C  and  D  meet  an  annular  space  is  dug  out,  30  inches  deep^ 
or  the  width  of  the  poling-boards;  in  this  space  the  concrete 
arch  is  built  on  centers  in  3O-inch  sections. 

The  steel  poling-boards  referred  to  are  made  of  No.  12  plate, 
2  feet  by  2  feet  6  inches  in  plan,  and  on  each  of  the  four  sides 
is  riveted  a  2  x  2  x  ^-inch  angle,  each  drilled  for  four  bolt-holes, 
used  in  connecting  the  plates.  -In  operation,  four  crown-plates 


Longitudinal        Section 
of  Heading. 


Cross       Section. 

FIG.    84. — East    Boston    Tunnel ;    Atlantic    Avenue    Station :    Method  of 
Building  Roof-arch. 

are  inserted  endwise  at  the  top  of  heading  A  and  bolted  to- 
gether and  to  the  rear  plates.  The  lateral  enlargement,  5  feet 
high  and  30  inches  wide,  is  roofed  in  a  similar  way  for  every  2 
feet  gained.  Normally,  the  advance  heading  is  kept  about  10 
feet  in  advance  of  the  arch  ring. 

All  the  material  from  the  headings  A  and  B  and  the  lateral 
drifts  C  is  removed  on  muck  cars  running  in  the  heading  B ; 
the  spoil  from  the  drifts  D  is  passed  down  to  cars  in  the  bottom 
side  drifts. 

The  arch-ring  centers  were  built  in  3O-inch  sections,  and  the 
lagging  is  left  off  the  ribs  at  the  crown.  A  special  floor  is  con- 


162 


MODERN    TUNNEL    PRACTICE 


SUBWAYS,    OR    UNDERGROUND    RAILWAYS  163 

structed  for  the  concrete  cars,  as  the  arch  work  progresses,  and 
at  the  level  of  the  top  deck  of  the  shield  through  which  the  cars 
must  pass  on  their  way  through  the  standard  tunnel  section. 
This  is  about  2  feet  below  the  floor  of  heading  A.  The  cars 
were  dumped  on  this  floor  and  the  concrete  was  shoveled  4n 
by  hand,  working  from  the  springing  line  to  the  crown.  The 
key  was  built  by  passing  the  concrete  in  endwise  over  the  for- 
ward center-rib.  The  steel  plates  were  left  in  place.  A  5-foot 
section  of  arch  was  constructed  every  24  hours. 

The  earth  core  was  removed  as  a  final  operation,  from  several 
benches ;  taking  the  material  out  under  air-pressure  and  passing 
it  through  the  air-locks.  The  invert  was  built  in  sections  as 
this  core  was  removed. 

Buda-Pest  Subway — This  line  is  historically  interesting  as 
being  the  first  underground  city  railway  operated  by  electricity. 
This  double-track  railway  is  about  two  miles  long  and  runs 
under  the  center  of  a  broad  street.  It  was,  consequently,  con- 
structed in  an  open  cut  in  1895;  Siemens  &  Halske,  of  Berlin, 
designing  the  electrical  equipment. 

The  typical  cross-sections  shown  in  Fig.  85  are  those  of  a 
dry-ground  section  and  a  deeper  section  where  the  excavation 
penetrates  below  the  water-line  in  the  ground.  In  the  latter 
case  every  precaution  has  been  taken  to  exclude  water  from  the 
subway.  The  asphalt  felt  employed  for  this  purpose  was  ap- 
plied in  sheets  in  two  layers,  each  sheet  being  about  31 J  inches 
wide  and  laid  to  break  joints.  On  the  under  side  these  sheets 
were  painted  with  a  sticky  natural  asphalt,  and  the  upper  side 
was  coated  with  fluid  asphalt. 

The  invert  shown  was  only  used  for  a  short  distance,  where 
ground-water  was  encountered.  The  drain-pipes  under  the 
center  of  each  track  drain  into  small  reservoirs  at  each  station, 
where  the  water  is  pumped  from  them  by  small  electric  pumps. 

New  York  Rapid  Transit.— Without  entering  into  the  detail 
of  the  history,  route,  etc.,  of  the  Rapid  Transit  Railway  now 
nearing  completion  in  New  York,  some  of  the  standard  cross- 
sections  are  here  given. 

The  plan  and  section  of  the  four-track  subway  shown  in  Fig. 


164 


MODERN    TUNNEL    PRACTICE 


86  requires  little  explanation.  The  same  type  of  construction 
applies  to  the  bulk  of  the  two  and  three-track  sections.  The 
form  is  rectangular,  and  it  is  made  up  of  transverse  bents  of 
steel  columns  and  roof  beams,  with  side  walls,  roof  and  floor  of 
concrete.  The  interior  columns  are  built  up,  while  the  side 


Waltr  Proofing... 


..:-.. 


777/s  Roof  Construct/on  if 
to  be  used  where  extra 
h  is  required  topers} 
s  across  Top  of 
Structure. 


Part    Plan. 

FIG.  86. — New  York  Subway :  Plan  and  Section,  Four-track  Line. 

columns  are  I-beams;  the  roof  is  supported  by  rolled  I-beams. 
The  entire  four  sides  of  the  section  are  preserved  from  seepage 
by  a  layer  of  waterproof  material  imbedded  in  the  concrete. 
The  double-track  rock  and  earth  sections  are  25  feet  wide 


SUBWAYS,    OR    UNDERGROUND    RAILWAYS 

in  the  clear  and  18  feet  high  at  the  crown,  as  shown  in  Fig.  87. 
In  each  case  the  tunnel  is  lined  with  concrete. 

Open-cut  Work,  New  York  Rapid  Transit  Railway. — As  an 
illustration  of  deep  open-cut  work  in  subway  construction,  a 
sketch  plan  is  here  given  showing  the  method  adopted  in  build- 
ing a  portion  of  the  New  York  Rapid  Transit  Railway. 

In  this  section  the  subway  excavation  had  to  be  made  unus- 
ually wide  to  provide  for  the  station  and  a  fifth  or  switching- 
track.  The  excavation  extended  to  a  depth  of  about  35  feet, 
with  the  bottom  10  to  15  feet  in  rock. 

The  sequence  of  operation  was  as  follows :     The  trench  A 


FIG.  87. — New  York  Subway :  Standard  Earth  and  Rock  Sections. 

was  first  opened  on  the  south  side  of  the  street  down  to  sub- 
grade  and  wide  enough  to  permit  the  erection  of  two  bays  of  the 
steel  work.  This  trench  was  sheeted  and  braced  in  the  usual 
manner,  and  the  two  bays  of  the  tunnel  were  completed.  The 
next  step  was  to  start  the  transverse  drifts  B,  each  about  12 
feet  wide  and  50  feet  apart,  and  long  enough  to  reach  beyond 
the  column  of  the  fourth  bent  of  steel  work.  The  top  of  these 
drifts  was  kept  well  above  the  subway  roof  line  and  the  bottom 
was  carried  to  the  rock,  each  drift  being  well  timbered  and 
sheeted.  When  a  number  of  these  drifts  had  been  completed 
the  north  ends  were  connected  by  the  longitudinal  drift  C  with 


1 66 


MODERN    TUNNEL    PRACTICE 


the  same  top  and  bottom  level  as  the  transverse  drift.  Then 
these  drifts  B  and  C  were  deepened  through  the  rock  to  sub- 
grade,  and  the  concrete  floor  was  laid  in  C,  and  on  this  was 
erected  the  fifth  row  of  columns. 

The  next  operation  was  to  widen  drift  B  so  as  to  permit  the 
placing  of  the  25-foot  roof  beams  connecting  the  third  and 
fifth  rows  of  columns.  This  widening  was  done  by  breaking 
down  both  sides  of  the  drift  under  poling-boards  driven  ahead 
and  supported  by  vertical  posts  until  the  headings  met  and  left 


Section     W-X. 
C.L.  of  Subway  Trvrcks 


Core  £&Lf 

Section      Y~2. 


C.I,  of  Subway  Trcrcte 
I 


^4-^-4J^-J,-.-_-Y|-14^1 

|»^<wflwl><K.*LQ«J 

6-  «  .  8-  .  |-^-|-T----r]-; 

r  «W^j  T.t.-=.-^^ajr  I 


FIG. 


. — New  York  Rapid  Transit  Railway :  Sketch-plan  Showing  Method 
of  Excavation  East  of  Fifth  Avenue. 


the  entire  space  between  the  drifts  open,  as  indicated  at  D.  The 
roof  beams  were  then  erected  and  the  rock  core  was  removed  to 
subgrade.  After  this  was  done  the  concrete  floor  was  put  in 
and  the  fourth  row  of  columns  was  set  up.  To  excavate  for  the 
fifth  bay  the  original  transverse  drifts  B  were  widened  out  until 
the  entire  space  was  cleared. 


SUBWAYS,    OR    UNDERGROUND    RAILWAYS 


i67 


As  fast  as  the  subway  roof  was  built,  brick  or  rubble  walls  or 
piers  were  erected  over  the  roof  beams  to  support  the  poling- 
boards,  and  all  open  spaces  were  packed  with  earth  and  stone. 
The  spoil  was  removed  on  a  track  laid  in  the  bottom  of  trench 
A,  with  transverse  tracks  laid  in  the  drifts  B  connecting  by 
turn-tables  with  the  main  track.  At  intervals  holes  were  left  in 
the  subway  roof,  and  through  these  the  muck  was  lifted  by  a 
Carson-Lidgerwood  cableway  and  deposited  in  carts  on  the 
street  surface.  The  final  operation  was  to  backfill  the  trench  A 
and  restore  the  street  surface. 

On  another  portion  of  this  line,  with  depth  of  excavation 


(a.) 


(to.) 


FIG.  89.— New  York  Subway:  Sketch-plan  Showing  Method  of  Work  Be- 
tween Fifth  and  Sixth  Avenues. 

varying  from  25  "to  39  feet,  and  the  lower  10  to  27  feet  in  rock, 
a  somewhat  different  method  of  construction  was  followed. 

The  opening  trench,  20  feet  wide,  was  sunk  to  subgrade  and 
in  this  the  south  bay  of  the  tunnel  was  erected  and  completed, 
except  for  some  holes  in  the  roof  for  extracting  material. 

At  intervals  of  about  TOO  feet  transverse  drifts,  12  feet  wide, 
were  driven  to  a  point  about  on  a  line  with  the  third  row  of 
columns.  This  drift  was  sheeted  and  timbered  and  had  its  top 
well  above  the  roof  line  and  its  bottom  on  the  rock.  A  pair  of 


l68  MODERN    TUNNEL    PRACTICE 

10  x  io-inch  beams  was  then  laid  on  the  subway  roof,  about 
over  the  second  row  of  columns,  to  form  a  support  for  the  rear 
ends  of  three  I-beam  needles  which  were  inserted  endwise  in 
the  drift,  about  5  feet  apart.  The  front  ends  of  these  I-beams 
were  supported  by  posts  resting  on  the  rock  bottom.  Wedges 
were  inserted  between  the  roof -sheeting  of  the  drift  and  the 
tops  of  the  I-beams,  and  these  were  driven  tight  so  as  to  take  the 
load  off  the  temporary  drift  struts  and  transfer  it  to  the  needles ; 
the  temporary  struts  were  then  removed. 

The  drifts  were  then  widened  by  removing  the  side  sheeting 
and  breaking  down  both  walls.  The  excavation  was  carried  on 
under  roof  poling-boards  driven  over  the  top  flanges  of  the 
needles.  When  the  excavation  had  proceeded  about  6  feet, 
another  I-beam  needle  was  inserted  parallel  to  the  first  and 
supported  in  a  similar  manner.  The  excavation  was  continued 
in  this  manner  until  a  sufficient  space  had  been  provided  to 
permit  the  excavation  of  the  rock  bottom  of  the  drift  to  sub- 
grade,  and  a  second  bay  of  the  tunnel  was  then  erected.  The 
widening  of  the  drifts  finally  cleared  the  whole  space  under  the 
needles,  and  the  second  bay  was  made  continuous. 

To  clear  the  space  for  the  third  bay  the  original  drifts  were 
extended  and  strutted,  as  before,  well  beyond  the  line  of  the 
fourth  row  of  columns.  Rubble  walls  were  first  built  on  the 
roof  of  the  subway  to  support  the  roof  poling-boards.  A 
timber  was  then  placed  parallel  and  close  to  each  of  the  three 
I-beams  and  was  jacked  up  until  it  took  the  roof  load  off  the 
needle.  The  three  I-beam  needles  were  then  slid  forward  into 
the  extension  of  the  drift  until  their  rear  ends  rested  on  the 
pair  of  10  x  io-inch  timbers  now  placed  over  the  third  row  of 
columns.  The  needles  were  supported  and  the  drift  widened 
as  before.  The  building  of  the  fourth  bay  was  simply  a  repeti- 
tion of  the  process. 

Atlantic  Avenue,  Brooklyn,  N.  Y — The  Atlantic  Avenue  sec- 
tion of  the  Long  Island  Railway  is  having  its  tracks  depressed 
and  put  into  a  subway.  The  standard  plans  adopted  for  this 
subway  are  here  shown  in  such  detail  that  little  description  is 
necessary. 


SUBWAYS,    OR    UNDERGROUND    RAILWAYS 


I7O  MODERN    TUNNEL    PRACTICE 

The  invert,  side  walls  and  roof  are  made  of  concrete.  The 
5-foot  arches  forming  the  roof  are  supported  by  transverse 
I-beams,  and  the  top  is  then*  waterproofed  as  follows :  After 
the  concrete  has  thoroughly  set  and  is  well  dried  out  by  the 
sun,  the  upper  surface  "is  swabbed  over  with  hot,  melted, 
medium  hard  coal-tar  pitch  of  a  somewhat  softer  grade  than 
that  used  for  roofing  purposes,  or  such  as  will  soften  at  a  tem- 
perature of  60°  F.,  and  melt  at  a  temperature  of  100°  F."  In 
this  pitch  the  oil  distilled  from  it  shall  have  "a  specific  gravity 
of  1.105."  The  pitch  is  put  on  until  it  has  a  uniform  thickness 
of  not  less  than  1-16  inch.  Immediately  upon  the  first  coat  and 
while  it  is  still  melted,  is  laid  a  covering  of  single-ply  roofing 
felt,  lapping  at  least  4  inches  on  all  cross- joints  and  at  least  12 
inches  on  all  longitudinal  joints.  The  felt  is  at  once  covered 
with  a  uniform  thickness  of  the  pitch,  and  upon  that  is  laid  a 
second  covering  of  roofing  felt,  which  is  also  covered  by  not 
less  than  1-16  inch  of  pitch.  This  waterproofing  extends  over 
the  ends  and  down  the  sides,  as  shown  on  the  cross-section. 
After  the  waterproofing  is  thoroughly  hardened  a  i-inch  layer 
of  Portland  cement  mortar  is  uniformly  spread  over  it  with  a 
trowel.  This  mortar  is  laid  in  5-foot  squares,  alternately,  for 
the  purpose  of  providing  for  expansion  and  contraction. 

At  intervals  of  30  feet  ventilator  wells  are  provided  leading 
to  the  street  surface,  and  at  intervals  of  15  feet  refuge  niches 
are  built  into  the  concrete  side  walls.  At  every  900  feet  special 
niches  are  made  in.  which  to  install  the  electro-pneumatic  sig- 
nals for  train  operation.  The  side  walls  contain  throughout 
their  entire  length  imbedded  ducts  for  electric  wires,  with  man- 
holes at  intervals  in  which  the  ducts  terminate. 


CHAPTER  IX 

SPECIAL  TUNNEL-BUILDING   PLANT 

Cascade  tunnel  plant — Scraper-loading — Automatic  dump  at  shafts — Dump- 
ing wagon — Cement-mortar  car — Walker's  detaching  hoist-hook — 
Concrete-mixer. 

The  success  or  failure  of  a  contractor  depends  largely — if 
not  entirely — upon  his  experience  and  skill  in  organizing  his 
working  force,  and  upon  the  intelligence  he  displays  in  devis- 
ing or  adopting  means  for  reducing  the  labor  cost  of  work  per- 
formed, and  at  the  same  time  hastening  completion.  This  con- 
tractor's plant  covers  a  multitude  of  items,  the  bulk  of  which 
are  familiar  to  both  engineers  and  contractors.  But  nearly 
every  large  work  also  demands  special  appliances  for  expedit- 
ing or  cheapening  work,  and  some  of  these  appliances  are  here 
illustrated  and  described,  rather  as  a  hint  to  the  contractor  than 
as  an  attempt  to  describe  the  multitude  of  devices  of  this  nature 
used  in  American  practice. 

Special  Plant  at  Cascade  Tunnel — In  an  article  upon  this  tun- 
nel John  F.  Stevens,  M.  Am.  Soc.  C.  E.,  then  chief  engineer 
of  the  Great  Northern  Railway,  describes  some  of  the  special 
plant  employed. 

The  tunnel  itself  is  in  rock,  single  track,  13,813  feet  long, 
with  the  section  shown.  In  excavation  the  arch  section  was 
first  taken  out  to  the  full  section  of  10  x  20  feet,  and  the  bench 
was  removed  in  two  lifts. 

To  facilitate  the  removal  of  rock  from  the  heading  and 
the  top  lift  of  the  bench,  a  traveling  platform,  or  "jumbo,"  was 
erected,  as  shown  in  Fig.  91 ;  the  broken  rock  being  wheeled 
onto  this  and  dumped  through  chutes  into  the  muck-cars  which 
could  run  beneath  it.  To  load  large  masses  of  rock  onto  flat- 
cars,  a  6-ton  capacity  hoisting  plant,  run  by  compressed  air,  was 

171 


MODERN    TUNNEL    PRACTICE 


SPECIAL    TUNNEL-BUILDING    PLANT 

installed  on  a  platform  beneath  the  main  platform  of  the 
"jumbo."  This  same  hoisting  engine  was  employed  in  mov- 
ing the  "jumbo"  back  from  the  face  during  a  blast. 

This  tunnel  was  lined  throughout  with  concrete,  nowhere 
less  than  24  inches  thick,  only  such  timbering  being  allowed  to 
remain  as  it  was  unsafe  to  move.  As  it  was  imperative  that  the 
placing  of  the  concrete  should  not  in  any  way  interfere  with  the 
driving  of  the  tunnel  a  special  concreting  apparatus  was  de- 
vised, as  shown  in  Fig.  91.  This  platform  was  erected  in  sec- 
tions 500  feet  long,  and  it  was  reached  by  an  incline  up  which 
the  concrete  cars  were  hauled  by  an  air-hoist  and  cable.  While 
each  500  feet  of  tunnel  was  being  concreted,  the  advance  500 
feet  of  platform  was  being  erected  with  its  own  incline.  The 
side  walls  were  built  in  sections  of  8  to  12  feet  in  length,  the 
weight  of  the  timber  arch  being  gradually  transferred  from  the 
plumb  posts  to  the  side  walls.  The  arch  sections  were  12  feet 
long,  4xi6-inch  plank  being  used  for  the  center-ribs.  As 
each  12  feet  was  completed,  the  centering  was  advanced  bodily 
12  feet  on  dollies  and  jacked  up  to  the  proper  elevation.  The 
concrete  was  mixed  on  planks  installed  at  each  portal,  the  pro- 
portions being  i  part  Portland  cement,  3  parts  sand,  and  5 
parts  broken  rock.  The  concrete  cars  were  hauled  to  the  foot 
of  the  incline  by  electric  motors.  The  average  monthly  prog- 
ress of  the  concreting  was  1,115  lineal  feet  of  tunnel;  the  best 
daily  progress  was  32  feet. 

All  hauling  out  of  muck  and  hauling  in  of  concrete  was  done 
by  electric  motors.  Eight  of  these  motors  were  in  service,  and 
one  of  these  motors  hauled  trains  of  16  to  20  loaded  dump-cars 
of  i  cubic  yard  capacity  each;  it  did  this  up  a  1.7%  grade  at  a 
speed  of  10  miles  per  hour.  The  track  was  double,  2-foot 
gage,  laid  with  second-hand  5O-lb.  rails  on  wooden  ties.  The 
track  system  was  equipped  with  split  switches,  electric  target- 
lamps,  etc.,  and  Mr.  Stevens  ascribes  much  of  the  success  met 
with  in  hauling  the  material  such  long  distances  to  the  care 
exercised  in  the  installation  of  this  track  and  to  the  heavy  ma- 
terial used  in  building  the  muck-car  trucks. 

Nearly  1,000  16  c.  p.  electric  lamps  were  used  in  the  tun- 


MODERN    TUNNEL    PRACTICE 

nel,  boarding  camps,  offices,  etc.  Electricity  was  generated  by 
eight  dynamos  aggregating  3OO-kw.  minimum  capacity. 
These  dynamos  were  driven  by  four  automatic  high-speed 
steam  engines. 

The  foul  air  was  exhausted  from  the  headings  through  a 
24-inch  galvanized  iron  pipe  by  means  of  a  No.  9  Sturtevant 
fan,  running  at  1,700  revolutions  per  minute.  These  exhaust 
pipes  were  made  in  1 6- foot  sections,  bolted  together  by  cast- 
iron  rings  with  friction-paper  washers  between  the  rings.  As  a 
rule  the  ventilation  was  excellent,  from  10  to  20  minutes  being 
sufficient  to  clear  the  heading  after  a  blast.  The  large  amount 
of  air  liberated  by  the  drills,  hoists  and  pumps  added  mater- 
ially to  the  supply  of  fresh,  cool  air. 

At  each  portal  large  power  houses  were  erected.  The  plant 
at  the  east  end  included : 

i   Ingersoll-Sargent  duplex  compressor 18  x  24  ins. 

i   Rand  duplex  Corliss  valve  compressor 20  x  36  ins. 

I   Buckeye  high-speed  engine 12x16  ins. 

i   Chandler  &  Taylor  high-speed  engine 13  x  14  ins. 

6  150  horse-power  boilers. 

Pumps,  water  heaters,  dynamos,  fans,  etc. 

At  the  west  portal  the  plant  included : 

i   Ingersoll-Sargent  duplex  compressor 18  x  24  ins. 

i   Buckeye  high-speed  engine ...12x16  ins. 

i   Chandler  &  Taylor  engine 13  x  14  ins. 

3   150  horse-power  boilers,  with  pumps,  etc.,  as  above. 

The  compressed  air  was  carried  to  the  work  in  a  6-inch 
wrought-iron  pipe,  and  distributed  at  the  headings,  through 
manifolds,  to  the  drills,  air  hoists,  pumps,  etc. 

The  pumps,  driven  by  compressed  air,  were  in  duplicate,  to 
avoid  delay  or  danger  from  accident.  The  considerable  annoy- 
ance caused  by  the  freezing  up  of  the  air-valves  of  the  pumps 
was  partly  eliminated  by  the  introduction  of  traps;  but  this 
trouble  was  not  serious  enough  to  warrant  reheating  the  air. 
During  the  last  year  of  the  work  at  the  east  end  over  one  mil- 


SPECIAL    TUNNEL-BUILDING    PLANT 


17S 


176  MODERN    TUNNEL    PRACTICE 

lion  gallons  daily  was  raised  no  feet  vertically  through  6,000 
lineal  feet  of  8-inch  pipe. 

Scraper  Loader. — In  driving  the  Kellogg  tunnel,  at  the 
Bunker  Hill  &  Sullivan  Mines,  in  Idaho,  a  scraper  was  used 
for  loading  the  debris  into  dump-cars.  This  is  described 
as  follows  by  Ulysses  B.  Hough,  the  engineer  of  the 
mines: 

The  tunnel  section  was  n  feet  high  and  9  feet  wide  in 
stable  rock ;  9  feet  high  by  8  feet  wide  in  the  clear,  in  timbered 
sections.  As  the  tunnel  was  about  9,000  feet  long  every  effort 
was  made  to  insure  rapid  progress.  Hand  shoveling  was  tried 
— by  day's  work  and  by  contract — with  little  difference  in  result 
in  removing  the  blasted  rock,  and  the  device  here  shown  was 
then  installed. 

A  single-drum,  double-cylinder  Bacon  hoisting  engine  was 
mounted  on  a  wooden  frame  arranged  to  permit  the  passage  of 
dump-cars  beneath  it,  these  cars  holding  i  cubic  yard  of  rock. 
In  front  of  this  frame  was  another  frame  with  an  inclined  floor 
toward  the  heading.  The  level  end  of  this  frame  would  allow 
two  cars  to  stand  under  it,  and  over  the  car  nearest  the  hoist 
was  an  opening  in  the  floor.  A  No.  I  scraper  was  employed 
in  hoisting  the  debris  up  the  incline  and  to  this  opening,  two 
scraper  loads  usually  filling  a  car.  When  the  first  car  was 
loaded  it  was  pulled  forward  and  the  second  car  was  filled  in 
like  manner.  Trains  were  made  up  50  to  100  feet  beyond  the 
hoist. 

The  gang  included  five  men :  One  at  the  hoist,  one  at  the 
dump-cars,  and  three  loaded  and  attended  to  the  scraper.  In 
2^  hours  these  men  moved  40  to  50  cubic  yards  of  waste,  or 
about  1 8  cubic  yards  per  hour. 

The  loading  platform  was  moved  by  a  special  car,  fitted  with 
four  jack-screws;  this  was  run  under  it  and  the  frame  was 
jacked  up  until  the  weight  rested  on  the  car;  the  frame  was 
then  pushed  back  to  permit  the  laying  of  new  rails.  The  hoist 
was  moved  in  a  similar  manner.  The  jack-screws  on  these  cars 
were  made  of  worn-out  drilling  machine  feed-screws.  The 
five  men  usually  moved  both  frames  in  five  minutes.  After 


SPECIAL    TUNNEL-BUILDING    PLANT 


177 


using  these  frames  for  fifteen  months  they  were  both  still  in 
good  condition. 

To  remove  the  rock  from  the  tunnel  a  4-ton  General  Electric 
Company's  motor  was  used.  This  motor  ran  on  a  24-inch 
gage  track ;  and  it  hauled  15  to  20  cars  at  a  time  on.  a  grade~of 
0.5  foot  and  0.3  foot  per  100  feet.  The  rails  weighed  30  pounds 
to  the  yard. 

The  smoke  and  gases  from  the  working  heading  were  re- 
moved by  a  No.  9  Sturtevant  fan,  exhausting  the  air  through  a 
22-inch  pipe  made  of  No.  18  galvanized  iron.  This  pipe  was 
made  in  1 8- foot  lengths,  with  all  seams  riveted  and  soldered. 


36'Cffblg 
Sheave 


K-"— i 
End  -of   Carriage, 
Enlarged. 


Side      Elevation. 

FIG.  93. — Automatic  Dump  for  Shafts. 


The  joint  was  made  by  inserting  one  pipe  in  the  other,  wrap- 
ping heavy  sheeting  about  the  joint  and  painting  with  coal-tar. 
This  plan  removed  the  gases  from  the  heading  in  15  to  20 
minutes,  even  with  8,000  lineal  feet  of  exhaust  pipe  in  use. 

Automatic  Dump  for  Shafts — Fairbanks,  Morse  &  Co.,  of 
Chicago,  111.,  manufacture  an  automatic  device  for  tripping  and 
dumping  buckets  at  the  head  of  a  shaft,  reducing  the  amount 
of  labor  ordinarily  required. 

Instead  of  the  usual  form  of  head-frame,  with  fixed  sheave 
above  the  mouth  of  the  shaft,  this  frame  is  made,  as  shown  in 
93,  with  an  incline  of  5  inches  to  I  foot.  Upon  this 


MODERN    TUNNEL    PRACTICE 

frame  is  mounted  a  steel  traveler  carrying  the  main  hoisting 
sheave. 

When  the  bucket  is  being  hoisted,  the  traveler  is  at  the  lower 
end  of  the  incline,  held  by  the  rails  bent  upward  to  form  a  stop. 
When  the  bucket  is  clear  of  the  shaft  a  stop  prevents  it  from 
rising  too  high ;  but  the  winding  of  the  cable  continues  and  the 
traveler  is  hauled  up  the  incline  and  is  automatically  caught  and 
held  by  a  pair  of  latches.  The  cable  is  then  paid  out  and  the 
bucket  is  lowered  to  the  dumping  floor.  This  platform  has  in 
it  a  slot  to  receive  a  loose  chain  attached  to  the  bottom  of  the 
bucket  and  carrying  a  disk  or  ball  at  its  end.  The  weight  of  the 
bucket  tilts  the  platform  and  the  bucket  is  inverted,  being  held 
to  the  platform  by  the  ball.  The  empty  bucket  is  then  hoisted 
again  and  the  latch  is  released,  the  carriage  runs  to  the  front 
of  the  incline  and  the  bucket  descends.  The  device  is  controlled 
by  the  one  man  at  the  hoisting  engine. 

Dumping  Wagon — The  illustration  sufficiently  shows  the 
construction  of  a  special  dumping  wagon,  made  by  the  Shad^ 
bolt  Manufacturing  Company,  Brooklyn,  N.  Y.  In  this  wagon 
the  body  is  balanced  over  the  hind  springs,  so  that  it  is  easily 
tilted  without  the  use  of  any  mechanism,  the  springs  resting  on 
a  bar  across  the  frame.  This  bar  pivots  in  steel  sockets  and 


FIG.  94. — The  'Shadbolt  Dumping  Wagon. 

turns  with  the  body ;  and  the  sockets  are  set  in  the  frame  sides  a 
sufficient  distance  in  front  of  the  rear  axle  to  throw  a  proper 
proportion  of  the  load  on  the  front  axle. 

In  dumping,  the  chain  passing  around  the  front  axle  takes 
up  some  of  the  jar,  prevents  the  body  from  striking  the  ground 
at  the  rear,  and  at  the  same  time  this  chain  automatically  pulls 


SPECIAL    TUNNEL-BUILDING    PLANT 


179 


the  hook  out  of  an  eye  in  the  tail-board  and  releases  the  latter, 
which  is  pushed  open  by  the  load.  This  wagon  was  successfully 
used  in  building  certain  sections  of  the  New  York  Rapid  Tran- 
sit Railway. 

Cement  Mortar-car  for  Lining  Tunnel — The  Mullan  tunneVoh 
the  Northern  Pacific  Railway,  was  relined  with  masonry  in 
1894,  to  replace  the  old  timber  lining.  H.  C.  Relf,  C.E.,  de- 
scribes this  work,  and  from  his  paper  in  the  Journal  of  the 
Association  of  Engineering  Societies,  for  August,  1894,  the 
following  matter  is  taken  relating  to  some  of  the  plans  used. 

The  tunnel  is  3,850  feet  long,  single-track ;  the  clear  dimen- 
sions in  the  lined  tunnel  being  16  feet  wide  and  20  feet  high  at 
the  crown.  The  masonry  includes  concrete  side  walls,  24 


1 

L 

£ 
i 

I 
1 

,'   ''        '•          *^.X 

iCt-  u    31 

- 

- 

Laqqi/jg 

i 

2 

• 

~^ 

# 

Section  ,with  Concrete  Car 


With  Wall  Plate.  Without  Wall  Plate. 

Lonaitudinal  Section. 


FIG.   95.— Mullan  Tunnel:    Cement-mortar   Car,   and   Timbering  Used   in 

Relining  Tunnel. 

inches  thick,  surmounted  by  a  full  center  arch  of  three  to  four 
rings  of  brick.  This  required  the  removal  of  all  the  old  timber 
lining. 

The  work  was  done  in  /-foot  sections,  by  first  removing  one 
post  and  supporting  the  5-segment  arch  of  12  x  1 2-inch  timbers 
by  the  struts  5*  S,  Fig.  95.  After  clearing  away  any  backing 
and  excavating  for  the  foot  walls,  two  temporary  posts  FF 


180  MODERN    TUNNEL    PRACTICE 

were  set  up  and  fastened  by  hook-bolts,  and  a  lagging  was  built 
to  hold  the  concrete.  Several  of  these  7-foot  sections  were  pre- 
pared at  a  time,  each  being  separated  by  a  5-foot  section  of  the 
old  timbering. 

The  cement-car  shown  was  then  run  in,  and  by  means  of  a 
chute  enough  cement  mortar  ( I  cement  to  3  sand)  was  run 
into  each  section  to  make  an  8-inch  layer  of  concrete.  As  the 
car  passed  on  to  the  next  section,  enough  broken  stone  was 
shoveled  into  the  8-inch  layer  to  take  up  all  the  mortar.  The 
walls  were  thus  built  in  8-inch  layers,  and  in  10  to  14  days  they 
were  sufficiently  set  to  hold  the  arch.  The  wooden  arches  were 
then  allowed  to  set  on  the  new  walls,  and  the  remaining  5-foot 
sections  were  cleared  of  timber  and  in  a  similar  manner  filled  up 
with  concrete.  The  average  progress  was  30  feet  of  side  wall 
in  one  working  day ;  or  about  45  cubic  yards,  costing  $8  per 
yard;  including  in  this  cost  all  labor  in  removing  old  timber, 
train  service,  lights,  tools,  engineering,  superintendence  and 
interest  on  plant. 

The  brick  arch  was  built  up  on  a  5-segment  center  supported 
by  posts,  wall-plates  and  sills.  This  arch  was  built  in  3  to  9- 
foot  sections,  depending  on  the  ground.  The  cement-car  was 
used  for  mixing  the  mortar.  This  brickwork  cost  $17  per  cubic 
yard ;  and  the  total  cost  of  the  new  lining  was  about  $50  per 
lineal  foot  of  tunnel. 

Steam-shovel  Operated  by  Compressed  Air In  driving  a  dou- 
ble-track tunnel  through  gneiss  and  mica-schist,  at  St.  Mary's 
Park,  on  the  New  York  Central  &  Harlem  River  Railroad,  the 
muck  in  the  tunnel  was  handled  by  a  steam-shovel  operated  by 
compressed  air. 

The  rock  was  removed  by  first  running  a  top-heading,  8x12 
feet,  through  the  tunnel,  and  then  taking  out  the  remaining 
rock  in  two  lifts,  working  from  the  top  down.  Two  rows  of 
holes  were  drilled  in.  each  bench  and  charged  and  fired  in  se- 
quence, using  6  pounds  of  dynamite  or  joveite  to  the  cubic  yard 
of  rock. 

The  heavy  muck  heap  resulting  was  attacked  by  a  Marion 
Model  No.  20  steam  shovel,  equipped  with  a  i-yard  dipper. 


SPECIAL    TUNNEL-BUILDING    PLANT 


181 


This  shovel  was  hauled  out  of  the  way  of  blasting  by  a  cable, 
operated  by  the  same  hoisting  engine  that  handled  the  muck 
cars  on  a  track  laid  parallel  to  the  shovel  track. 

The  muck  cars  had  a  capacity  of  about  5  cubic  yards,  jand 
they  averaged  about  2f  cubic  yards  of  solid  rock  per  load.  These 
cars  were  hauled  out  of  the  tunnel  in  trains  of  two  cars,  up 
an  incline  having  a  sufficient  grade  to  run  the  empty  cars  back 
again.  The  muck  was  lifted  in  skips  by  a  derrick  located  on  the 
side  of  the  approach  cut,  and  was  either  dumped  into  cars,  or 
on  a  heap  for  use  in  concrete  makiner. 

The  compressed  air  was  furnished  by  the  rock-drilling  plant, 


FIG.  96.— The  Walker  Detaching  Hook  for  Shaft-hoists. 

and  the  shovel  gave  perfect  satisfaction  in  its  working  in  the 
tunnel.  Its  crew  consisted  of  two  shovelmen,  four  pitmen, 
and  a  pit  boss. 

Walker's  Detaching  Hook — A  frequent  source  of  danger  in 
shaft  hoisting  is  the  overwinding  of  the  cage,  due  to  careless- 
ness or  accident.  To  obviate  this  danger,  the  Walker  detach- 
ing hook  is  now  largely  used  in  England. 

In  this  hook  the  lifting  rope  is  attached  to  the  shackle  A,  and 
the  cage  is  hung  from  the  connecting  link  B.  The  supporting 
ring  C  is  a  fixture  in  the  beam  at  the  top  of  the  head  gear.  The 
two  jaws  of  the  hook  work  on  a  center  pin  E,  in  such  manner 


1 82 


MODERN    TUNNEL    PRACTICE 


SPECIAL    TUNNEL-BUILDING    PLANT 

that,  in  case  of  overwinding,  the  load  tends  to  open  the  jaws 
and  release  the  center  pin  of  the  shackle  A;  though,  ordinarily, 
the  clamp  H  keeps  the  jaws  together. 

In  case  of  overwinding,  the  jaw-hooks  pass  freely  into  the 
ring  C;  but  the  projection  K  on  the  clamp  H,  on  coming1- in 
contact  with  the  bottom  flange  of  C,  holds  the  clamp  stationary 
and  allows  the  jaws  to  be  pulled  through  the  ring  C.  In  doing 
this  two  small  pins  /  /  are  sheared  off,  and  the  jaw-hooks  open 
and  catch  on  the  ring  C,  holding  the  cage,  and  at  the  same  time 
releasing  the  shackle  A  and  the  winding  rope  attached  to  it. 


'          m 

fj     •  '.|          ii  •"  1 1  r .."V'-.-  "-M   ••!   ,      •• 


FIG.  Q7a. — Cross-section  on  St.  Louis  Canal,  Showing  Arrangement  of  Ma- 
chinery During  Construction. 

Concrete  Mixer,  etc — In  the  construction  of  the  lined  and 
covered  canals  for  the  improved  drainage  of  New  Orleans,  La., 
the  comparatively  narrow  streets  of  the  old  city  required  spe- 
cial disposition  of  the  necessary  plant. 

The  cross-section  of  the  canal  on  St.  Louis  street  (Fig.  9/a) 
shows  the  general  arrangement  adopted  for  taking  away  the 
excavated  material  and  bringing  in  the  material  of  construction. 

The  concrete  mixer  employed  was  arranged  to  run  on  a 


1 84 


MODERN    TUNNEL    PRACTICE 


track  of  8-foot  gage,  supported  by  the  brace  timbers.  Beneath 
the  mixer  was  a  3<>inch  track  carrying  small  side-dump  cars, 
of  a  capacity  of  18  cubic  feet  each.  The  mixer  itself  consisted 
of  a  heavy  cast-iron  box,  in  which  revolved  in  opposite  direc- 
tions two  mixing  paddles.  The  dry  material  was  shoveled  into 
the  gaged  hoppers  and  dumped  directly  into  the  mixer  through 
bottom  doors  operated  by  levers.  The  sand  and  cement  came 
from  the  material  yard  in  skips,  these  latter  being  rilled  from 
the  cars  by  a  3-ton  American  hoist  traveling  derrick.  This 
derrick  was  also  used  for  lifting  the  bricks  required  and  hand- 


Plan. 


/\ 


1,000  1 

3ricks 

I'-' 

g 

Side  Elevation.  Cross  Section. 

FIG.  98.— Crates  for  Handling  Bricks. 

ling  the  heavy  roof  beams,  which,  in  the  larger  canals,  weighed 
one  ton  each.  The  trains  to  and  from  the  work  were  operated 
by  an  electric  trolley  system. 

The  bricks  were  made  near  Lake  Ponchartrain.  And  as 
these  bricks  were  taken  from  the  kilns  they  were  piled  on  spe- 
cial crates  (Fig.  98)  holding  1,000  bricks  each.  These  crates, 
with  the  bricks,  were  picked  up  by  a  derrick  and  loaded  upon 
barges,  each  barge  carrying  100,000  bricks.  This  barge  was 
towed  to  a  city  landing,  and  the  crates  and  bricks  were  again 
picked  up  and  deposited  directly  on  the  material  cars,  each 


SPECIAL    TUNNEL-BUILDING    PLANT  185 

car  carrying  4,000  bricks.  The  bricks  were  finally  dumped  on 
the  work  within  reach  of  the  bricklayers.  This  method  saved 
much  time  and  expense  in  avoiding  rehandling,  and  materially 
reduced  the  percentage  of  breakage. 


CHAPTER     X 

SOME  DATA  UPON  THE  COST  OF  TUNNELING 

Cost  of  hand-drilling  in  shaft-sinking — Cost  of  power-drilling  in  shaft- 
work — Cost  of  drifting  and  cross-cutting — Hand-work  in  tunnel  driv- 
ing— Diamond-drill  work — Cost  of  square-set  mine  timbering — Cost  of 
mine-hauling  by  compressed  air — Cost  of  concrete  tunnel-lining — 
Water-hauling  vs.  pumping  in  mines — Cost  of  driving  a  mine-heading 
— Cost  of  tunnel-driving  and  steam-shovel  work. 

While  the  probable  cost  of  performing  work  is  of  the  utmost 
importance  to  the  bidder  upon  public  works,  for  reasons  easily 
guessed  at,  reliable  data  as  to  this  cost  is  a  valuable  asset  to 
the  individual  contractor,  and,  as  a  rule,  he  .is  not  willing  to 
publish  it  for  the  benefit  of  others.  So  many  varying  factors 
also  enter  into  this  cost  that  experience  on  one  piece  of  work  is 
not  always  a  safe  guide  for  the  cost  of  other  and  seemingly 
similar  work.  But,  from  returns  of  cost  carefully  made  by 
engineers,  a  few  cases  have  been  here  selected,  chiefly  for  the 
purpose  of  showing  how  such  records  should  be  kept. 

Hand-drilling  in  Shaft  Sinking. — The  following  detailed 
record  of  shaft  sinking  at  the  Golden  Eagle  Mine,  Lassen  Co., 
CaL,  is  given  by  Mr.  E.  H.  Benjamin,  M.  Am.  Inst.  M.  E. 
This  shaft  was  commenced  at  the  4OO-foot  level,  and  was  sunk 
150  feet  below  that  point.  The  rock  was  hard  andesite,  with 
no  water.  The  shaft  was  /x  12  feet  in  the  clear;  timbered 
by  10  x  lo-inch  sawed  timbers,  plates  and  center-braces  dove- 
tailed in,  and  center  and  corner  posts  gained  in.  The  sets  were 
5  feet  apart  c.  to  c.,  filled  and  lagged  with  12  x  1 2-inch  lining 
set  3  feet  apart. 

The  work  was  completed  in  forty-seven  8-hour  shifts,  work- 
ing three  shifts  a  day  with  three  men  on  a  shift.  This  makes 
an  average  of  3.2  feet  per  shift,  hoisting  by  bucket  20  tons 
of  material  per  shift,  besides  timbering. 

1 86 


SOME  DATA   UPON   THE   COST   OF  TUNNELING  l8/ 

For  each  round  18  holes  were  drilled;  each  hole  3^  to  4  feet 
deep,  using  j-inch  steel;  No.  2  Giant  powder  was  used  for 
blasting;  and  the  ground  drilled  hard,  but  broke  well.  Mr. 
Benjamin  says  that  he  does  not  know  of  a  better  record  for 
hand-drilling  in  a  shaft. 

This  detailed  record  is  useful  for  purposes  of  comparison, 
and  as  showing  how  complete  a  record  of  this  kind  can  be 
made. 

DETAILED  RECORD  OF  SINKING  150  FEET  OF  SHAFT  AT  THE 
GOLDEN  EAGLE  MINE,  LASSEN  COUNTY,  CAL.,  1902. 


Detail.                Shifts. 
Miners    (9)                 423 
Topmen   (2)                   94 
Engineers    (2)               94 
Blacksmith   (i)             47 
Foreman  (i)                 47 

Wages,  or  Price. 
$3.00  per  shift. 
2.50 
3-00 
3-50 
$100.00  per  month. 

Totals.     Ci 
$1,269.00 
235-00 
282.00 
164.50 
172.30 

jst  per  ft. 
$8.460 
1.566 
1.880 
1.096 
1.149 

Total  labor   ....  705 

Timber  —  10,976  feet  B.  M. 
Lagging  —  2,250  feet  B.  M. 
Lining  —  2,270  feet   B.   M. 
Cord  wood,  block  G  —  5  cords 
Wedges  —  3,000 

QUANTITY. 

$13.00  per  M. 
0.035  per  piece 
14.00  per  M. 
3.00  per  cord 
o.oi  per  piece 

$2,122.80 

$142.69 
88.20 
31-78 
15.00 
30.00 

$14.151 

$0.951 
.588 

.212 
.100 
.2OO 

Total  timber 

$7Q7  67 

$2  O^I 

Wood,  Fuel  —  25  cords 
Oil  and   incidentals 

$3.00  per  cord 

$75-00 
15.00 

$0.500 
.IOO 

Total  power  cost 

$QO  OO 

$O600 

Coal  oil                    6  cases 
Candles                     6  cases 

$4.15  per  case 
6.40  per  case 

$44.90 
38.40 

$0.166 
.256 

Total  illumination 

$6?  to 

$O  422 

Powder                    600  Ibs. 
Fuse                     2,500  ft. 
Caps                        550 

$0.14  per  Ib. 
3.70  per  M. 
6.25  per  M. 

$84.00 
9-25 
344 

$0.560 
.O6l 
•023 

Total  explosives 

$9669 

$0644 

Total  cost  of  mo  feet  of 

shaft.  . 

$2.680.46 

$17.868 

Power  Drilling  in  Shaft  Sinking Mr.  E.  C.  Voorheis,  Super- 
intendent of  the  Lincoln  Gold  Mine  Development  Company, 
Amador  Co.,  CaL,  gives  the  following  data  in  power  drilling 
in  shaft  work,  in  1902. 


1 88  MODERN    TUNNEL    PRACTICE 

The  Lincoln  shaft  was  sunk  from  the  1,260- foot  level  to  the 
2,ooo-foot  level,  a  depth  of  740  feet.  The  ground  was  green- 
stone and  hard,  black  slate,  and  the  size  of  the  excavation  was 
8x  17  feet.  The  men  worked  in  8-hour  shifts.  The  drilling 
was  done  by  means  of  the  "Baby"  giant  drill;  the  average 
depth  of  each  hole  in  the  shaft  being  6  feet.  Hercules  powder, 
40%  nitroglycerine,  was  employed;  and  crude  oil,  at  $1.50  per 
barrel  of  42  gallons,  was  used  for  steaming.  To  sink  the  shaft 
3.864  blasting  holes  were  required,  or  5.2  per  foot  of  shaft. 

During  the  sinking  of  the  shaft  60,025  tons  of  water  were 
hoisted;  adding  to  this  9,456  tons  of  waste  makes  a  total  of 
69,481  tons  hoisted  to  the  surface. 

The  following  table  gives  the  labor  cost  of  sinking  the  shaft 
and  putting  in  the  timbers : 

COST  OF  SINKING  740  FEET  OF  SHAFT. 

Cost  per  ft. 

Quantity.      Class.  Wages,  or  Item  Cost.    Total  Cost,     of  Shaft. 

2,956  days        Labor  $2.75  per  8  hours          $7,129.00 

350  days        Day  foreman         4.00  per  8  hours  1,400.00 

282  days        Night  foreman      3.25  per  8  hours  916.50 


Total  labor  cost,  sinking  and  timbering $9,445.50  $12.76 

12,450  Ibs.  Hercules  powder  (16.8  Ibs.  per  ft.  shaft)  1,307.25  1.76 

35,800  ft.  Fuse  125.30  .17 

46  boxes  Lion  caps  46.00  .06 

2,400  Ibs.  Candles  288.00  .39 

148  sets  Timbers          207,200  ft.  at  $18  per  M  -3,729.60  5.04 

Total  cost  labor,  lumber,  powder,  etc $14,941.65  $20.18 

Total  labor  engineers,  blacksmiths,  framers,  etc.  6,224.00  8.41 

Total  cost  fuel  5,893.50  7.96 

Total  cost,  all  expenses  except  office $27,059.15  $36.56 

Drifting  and  Cross-cutting — From  this  same  shaft  a  cross-cut 
was  extended  642  feet,  passing  through  40  to  60  feet  of  black 
slate,  with  considerable  water;  and  then  two  drifts  were  driven, 
aggregating  483  feet  in  length.  This  work  was  done  with 
the  "Baby"  giant,  and  the  average  depth  of  each  drill  hole  was 
5  feet.  The  following  table  of  cost  was  furnished  by  Mr. 
Voorheis : 


SOME  DATA  UPON   THE   COST   OF  TUNNELING  189 

COST  OF  RUNNING  1,125  FEET  OF  DRIFTS  AND  CROSS-CUTS. 

Total        Cost 

Quantity.         Class.  Wages,  or  Item  Cost.  Cost.      Per  Ft. 

1,428  days     Labor  Miners,  $2.75  ;  car  men,  $2.50     $3,772.50 

168  days     Day  foreman       $4.00  per  lo-hour  day  672.00 

134  days     Night  foreman      3.25  per  lo-hour  day  435-5O 


Total  labor  cost $4,880.00  $4.153 

11,150  Ibs.     Powder    1,226.50  1.043 

26,500  ft.       Fuse    79-50  .068 

35  boxes     Lion  caps   35-QO  .030 

800  Ibs.     Candles    96.00  .082 


Total  cost  $6,317.00     $5.376 

3,258  holes  drilled,  or  2.77  per  foot ;  using  average  of  3.42  pounds  of 
powder  for  each  blasting  hole. 

Hand  Work  in  Tunnel-driving — The  following  cost  data  re- 
fer to  a  short  tunnel  on  the  W.  Va.  &  P.  R.  R.,  driven  in 
1891.  The  tunnel  was  only  624  feet  long,  and  was  driven 
through  a  soft  blue-clay  shale,  showing  little  stratification  and 
practically  dry.  The  tunnel  had  a  span  of  23  feet,  was  13  feet 
from  the  floor  to  springing  line,  and  the  arch  was  a 
full  center  of  n^  feet  radius.  The  heading  area  was  208 
square  feet;  bench  area,  299  square  feet,  or  507  square  feet  in  all. 

The  work  was  done  entirely  by  hand,  with  the  following 
force:  On  heading,  i  foreman,  8  miners,  6  muckers,  and  one 
boy;  on  bench,  I  foreman,  8  miners,  10  muckers  and  one  boy. 
Common  laborers  were  paid  $1.45  per  day,  and  miners  received 
$1.75  per  day  of  ten  hours. 

In  the  heading  three  sets  of  holes  were  drilled,  each  set 
consisting  of  4  holes  about  4  feet  deep.  Each  hole  was  loaded 
with  from  4  to  6J-pound  sticks  of  dynamite,  and  an  average 
advance  of  2.\  feet  was  made  in  each  blast.  A  derrick-car  was 
used  in  handling  the  muck,  and  also  for  handling  the  timbers, 
lagging  and  packing. 

The  bench  was  taken  down  in  4- foot  lifts,  two  half-depth 
blasts  being  made  for  each  hole.  Each  blast  consisted  of  4 
holes,  with  10  sticks  of  dynamite  to  an  outside  hole  and  15 
sticks  to  the  center  hole.  The  bench-progress  per  shift  was 
about  2^  feet. 

The  work  was  done  by  contract  at  the  following  cost  to  the 
railway  company : 


I9O  MODERN    TUNNEL    PRACTICE 

11,726  cubic  yards  excavation  at  $2.85 $33>4iQ 

742  cubic  yards  packing  at  $1.75 1,298 

256  cubic  yards  fallen  rock  at  $1.25 320 

303,000  ft.  B.  M.  timbering  at  $30.00 9,090 

Total  cost  of  624  lin.  feet  tunnel $44  127 

Cost  per  lin.  foot $70.70 

Cost  of  Driving  Heading — In  1899  the  cost  of  driving  a 
7  x  8- foot  heading  in  the  Melones  Mine,  Calaveras  Co.,  Cal.,  is 
given  as  follows  by  W.  C.  Ralston,  M.E. : 

This  heading,  or  adit,  was  2,608  feet  long,  with  a  grade  of 
3  inches  per  100  feet.  The  drilling  was  done  by  three  Inger- 
soll  Eclipse  drills,  run  by  an  Ingersoll-Sargent  Class  B  com- 
pressor ;  the  latter  was  operated  by  a  5-foot  Pelton  wheel  under 
a  head  of  470  feet.  The  rock  was  diabase,  brown  slate  and  talc 
schists,  requiring  timbering  on  some  lengths. 

The  working  force  of  29  men  was  divided  into  three  8-hour 
shifts  of  7  men  each.  No.  2  40%  Hercules  powder  was  used 
throughout;  and  after  each  blast  water,  under  200- foot  head, 
was  freely  used  in  condensing  fumes  and  cooling  the  air.  After 
eight  and  a  half  months  of  almost  continuous  use  the  total  cost 
of  repairs  and  extras  for  the  compressor  amounted  to  $21.32. 
The  total  cost  of  extra  parts  for  the  three  drills  was  $91.65. 

ACTUAL  COST  (EXCLUSIVE  OF  MANAGEMENT)  OF  2,608.5 
FEET  OF  TUNNEL  AND  DRIFTS,  7x8  FEET. 

Cost  per 

Totals.  Lin.  /•/. 

Labor,  including  timbering $19,501.46  $7-47 

2,000  Ibs.  powder,  No.  ij  at  16.6  cts 

25,550  Ibs.  powder,  No.  2,  at  11.9  cts 3,405.65  1.30 

75,000  ft.  fuse,  at  51.7  cts ....! 

200  boxes  caps,  at  60  cts '. 500.20  .19 

333^  cords  wood,  at  $5.00 1,667.50  .63 

40  ins.  water  and  tender,  at  15  cts 828.50  .32 

11,591  Ibs.  coal,  at  $15  per  ton  and  freight 179-43  .06 

8,466  ft.  timbering,  at  $20  per  M 169.32  .06 

3,040  Ibs.  candles,  at  7M>  cts 262.04  -io 

21,555  Ibs.  steel  rails,  il/4  to  2^/4  cts 567-62  .22 

Air  pipe,  n  in.,  at  18  and  30  cts 

Air  pipe,  3  in.,  at  22  cts 

Water  pipe,  2  in.,  at  11^/4  cts .' 1,042.45  .45 

Hay,  iY2  cts. ;  barley,  .019  cts 267.16  .10 

Steel,  drill  parts,  oil,  tools,  etc 316.92  .12 

Total    $28,708.25 

Actual  cost  per  lin.  ft $1.1.02 

The  air  and  water  pipe  were  in  large  part  reused,  hence  comparatively 
small  cost  per  lin.  foot. 


SOME  DATA   UPON   THE   COST  OF  TUNNELING  19! 

Tunnel  Work  on  Ohio  Residency,  Pittsburg,  Carnegie  &  West- 
ern R.  R.* — This  road  is  characterized  by  exceedingly  heavy 
work  in  grading;  and  construction  was  still  in  progress  in  1904. 

The  double-track  tunnel  section  is  shown  in  Fig.  100.  The 
usual  method  of  attack  adopted  was  to  drive,  at  the  same  time, 
two  7  x  8-foot  headings,  the  floor  of  the  headings  being  about 
I2j  feet  above  grade.  As  these  headings  advance,  the  material 
between  them  is  blasted  out  and  the  arch  area  cleared  through 
from  portal  to  portal.  The  12^-foot  bench  is  then  removed. 
Two  steam  drills  are  operated  in  each  heading,  without  inter- 
ference. The  excavated  material  is  run  out  on  small  dump 
cars,  and  is  dumped  into  a  chute  that  leads  to  cars  on  the  grade 
below. 


FIG.  loo.— P.  C.  &  W.  R.  R.  Standard  Tunnel  Section. 

The  cost  of  driving  by  han<^  a  7  x  8-foot  heading  in  sand- 
stone is  given  as  follows : 

Labor,  per  shift $18.20 

Explosives 3.84 

Repairs 90 

Light 32 


Total $23.26 

As  each  shift  removed  6.2  cubic  yards  of  heading,  the  cost 
was  $3.75  per  cubic  yard. 

^Engineering  News,  May  21,  1903. 


MODERN    TUNNEL    PRACTICE 

In  another  sandstone  tunnel  where  power  drills  were  used, 
the  cost  of  driving  100  feet  of  a  full-sized  heading,  running  15 
cubic  yards  to  the  lineal  foot,  was  as  follows,  per  lineal  foot  of 
heading : 

Labor $2,527-45 

2,000  Ibs.  dynamite,  40  per  cent.,  at  12  cts 260.00 

470  gals,  kerosene  oil,  at  12  cts 56.40 

1,875  gals,  gasolene,  at  12  cts 225.00 

3,000  bushels  coal,  for  compressor,  at  9  cts 270.00 

Machine  and  lubricating  oil 62.50 

Blacksmithing   150.00 

4I.6JQ  ft.  B.  M.  timber,  at  $23 957-93 

Total  cost  loo  lin.  ft $4,509.28 

Cost  per  lin.   ft.   including  timber $45.09 

Cost  per  cubic  yard,  including  timber 3-°6 

The  timber  was  in  rings  of  12  x  1 2-inch  stuff,  4  feet  c.  to  c., 
lagged  with  4-inch  plank.  This  timbering  is  shown  in  Fig. 
TOO.  The  ribs  are  usually  spaced  3  feet  c.  to  c. ;  though  this 
was  made  2  feet  in  soft  ground  and  4  feet  in  hard  ground.  The 
tunnel  timbering  was  Georgia  pine,  and  in  one  tunnel  the  cost 
was  as  follows : 

Cost  per  iwoft.B.M. 

Georgia  pine,  f .  o.  b.  cars $23.60 

Hauling  6  miles    3.00 

Cost  of  framing 5.00 

Cost  of  erecting  and  bracing 3.00 


Total  cost  in  place $34-6o 

To  put  in  the  packing  over  the  lagging  cost,  in  some  cases, 
80  cents  per  cubic  yard.  The  carpenters  who  did  the  fram- 
ing received  $3.00  per  lo-hour  day,  and  the  laborers  who  did 
the  erecting  received  $1.50  for  a  similar  day.  In  this  case  the 
framing  and  erecting  cost  was  excessive,  owing  to  the  im- 
proper division  of  labor  and  doubling  of  "bosses." 

Steam  Shovel  Work — As  shovel  work  may  be  advantageously 
used  in  the  approaches  to  tunnels,  some  late  notes  upon  the 
cost  of  work  of  this  type  are  here  given  from  experience  on 
the  Ohio  Residency,  Pittsburg,  Carnegie  &  Western  R.  R. 

With  a  35-ton  Vulcan  traction  shovel,  with  I  cubic  yard 
dipper,  1 1  minutes  were  consumed  in  loading  6  dump  cars  of 


SOME  DATA   UPON   THE   COST   OF  TUNNELING 

3  cubic  yards  nominal  capacity  each.  To  haul  this  train  800 
feet  to  the  dump  and  return,  by  a  contractor's  locomotive,  re- 
quired 6  minutes.  Dumping  one  car  at  a  time  through  a  trestle 
took  3  men  3  minutes  for  the  6  cars. 

The  force  employed  at  the  shovel  was :  i  boss,  i  craneman,. 
I  engineer  on  shovel,  i  fireman,  i  engineer  on  locomotive,  I 
brakeman  on  train,  i  engine-driver  on  water-supply  pump,  3, 
pitmen,  6  drillers,  i  blacksmith  and  2  dumpmen. 

This  crew  averaged  500  cubic  yards  of  material  excavated 
in  a  10-hour  day,  the  material  being  mostly  soft  shale,  with 
a  face  10  to  15  feet  high.  Though  the  shovel  is  apparently 
standing  idle  one-third  the  time,  there  is  not  so  much  lost  time 
as  appears.  During  the  absence  of  the  cars  the  shovel  is  moved 
forward,  requiring  about  3  minutes  to  move  4  feet  and  to 
block  up. 

Concrete  Tunnel  Lining — In  1903  a  double-track  tunnel  275, 
feet  long,  and  near  Peekskill  on  the  New  York  Central  Rail- 
way, was  driven  and  lined  with  concrete,  and  the  following 
statement  of  the  cost  is  made  by  George  W.  Lee,  M.  Am.  Soc. 
C.  E.,  engineer  for  the  contractor. 

The  tunnel  section  (Fig.  99)  was  enlarged  from  6  inches  to 
3  feet  outside  the  concrete  section,  the  rock  being  the  usual 
rock  of  the  Hudson  River  valley.  As  soon  as  the  foundation 
trenches  had  been  excavated  and  concreted,  platforms  25  feet 
square  were  erected  at  each  end  of  the  tunnel  and  at  the  level 
of  the  springing  line  of  the  arch.  Near  each  platform  a  stiff-leg 
derrick  with  a  4<>foot  boom  was  then  set  up,  between  the  ma- 
terial track  and  the  mixing  platforms,  to  handle  the  skips.  This 
material  track  ran  under  the  platform  and  through  the  tunnel, 
and  a  turnout  was  laid  beyond  each  portal  for  switching  pur- 
poses. Steam  was  furnished  to  the  hoisting  engines  by  a 
60  h.-p.  boiler  on  wheels. 

The  bench-wall  forms  were  made  in  1 2-foot  sections,  with 
plates  and  sills  of  4  x  6  inches,  and  studs  of  4  x  4-inch  hemlock, 
spaced  3  feet  c.  to  c.  The  sheathing  was  2-inch  dressed  and 
matched  spruce.  Four  of  these  forms  were  set  in  place  on 
each  foundation  at  the  center  of  the  tunnel  length;  and  wheel- 


194 


MODERN    TUNNEL    PRACTICE 


barrow  runways  were  laid  on  bents  leading  to  both  mixing 
platforms.  These  bench  walls  were  not  carried  back  to  the 
rock;  back  forms  of  i-inch  hemlock  were  used,  and  the  space 
behind  the  walls  was  filled  with  spawls,  to  allow  the  consider- 
able seepage  from  the  rock  to  collect  and  run  out  at  the  "weep- 
holes"  provided  in  every  15  feet  of  the  bottom  part  of  the  walls. 
While  the  concrete  was  being  filled  into  these  forms,  other 
sections  were  being  set  up  at  each  end  of  this  central  part.  The 


k- — si'ii" 

FIG.  99. — Peekskill  Tunnel :  Concrete  Lining. 

forms  for  the  bench  walls  were  removed  in  24  hours  after  the 
concrete  had  been  laid,  and  the  surface  was  rubbed  smooth  with 
wooden  floats.  The  bench  walls  terminated  in  sandstone 
portals. 

Arch  forms  were  then  erected  for  a  distance  of  96  feet  in 
the  center  of  the  tunnel,  and  the  lagging  was  laid  in  1 2-foot 
sections,  at  first  extending  only  3  feet  above  the  springing  line. 
Runways  were  laid  over  the  lower  chords  of  the  ribs,  the  latter 
being  spaced  4  feet  c.  to  c.  On  the  upper  portion  of  the  ring 
the  concrete  was  first  shoveled  on  a  platform  laid  about  2  feet 
below  the  crown,  and  then  passed  in  onto  the  lagging,  which 
was  here  in  4-foot  lengths.  The  arch  section  was  water- 
proofed by  six  layers  of  tar  paper,  laid  in  hot  tar,  and  the  space 
above  the  arch  was  filled  in  with  spawls. 

The  foundations,  bench  walls  and  arch  were  made  of  i  part 


SOME  DATA  UPON   THE   COST   OF  TUNNELING  IQ5 

cement,  2  parts  sand,  and  4  parts  of  crusher-run  stone,  of  a 
size  passing  through  a  i-inch  ring.  The  quantities  were: 
Foundations,  200  cubic  yards;  bench  walls,  692  cubic  yards; 
arch-ring,  932  cubic  yards. 

The  total  cost  of  the  concrete  work  is  given  as  follows : 

Cement,  at  $i .63 $5, 755-5° 

Sand,  at  75  cts 662.94 

Crushed  stone,  at  80  cts 1,303.20 

Lumber,   total    i, 497-71 

Coal    ii8.73 

Oil    16.12 

Nails,  spikes,  etc 224.39 

Tools    .... 181.10 

Freight  on  cement,  stone,  etc 3,089.86 

Labor,  including  superintendent,  foreman,  etc 8,036.31 

$20,885.76 
Average  cost  of  concrete  $10.72  per  cubic  yard. 

Water  Hoisting  vs.  Pumping  in  Mines. — An  interesting  paper 
on  "Methods  and  Cost  of  Water  Hoisting  in  the  Pennsylvania 
Anthracite  Region"  was  read  before  the  American  Institute  of 
Mining  Engineers  by  R.  V.  Norris,  M.  Am.  Inst.  M.  E.  This 
paper  is  very  fully  illustrated,  and  those  interested  are  advised 
to  read  the  original  paper  in  the  Proceedings  of  the  Society,  or 
its  reprint  in  Engineering  News  of  April  9,  1903.  Some  ab- 
stracts from  the  paper  are  here  given,  showing  the  general 
system  and  the  results. 

The  removal  of  mine  water  by  hoisting  in  tanks  instead  pof 
pumping  is  rapidly  coming  into  favor  in  the  anthracite  region 
of  Pennsylvania,  about  fourteen  large  collieries  being '  so 
equipped.  Some  of  the  shafts  so  cleared  are  1,500  feet  deep. 

The  hoisting  tanks  are  cylindrical  or  semi-cylindrical,  tak- 
ing in  water  through  chock-valves  at  the  bottom  and  discharg- 
ing in  various  ways,  usually  automatically.  These  tanks  were 
first  attached  to  the  bottom  of  the  regular  shaft  carriages ;  but 
the  objection  to  this  was  the  limiting  of  their  use  to  the  night 
shift,  with  a  corresponding  loss  in  capacity.  The  present  prac- 
tice is  to  locate  these  tanks  in  a  special  water  compartment, 
permitting  constant  service,  whether  in  a  vertical  or  inclined 
shaft. 


196  MODERN    TUNNEL    PRACTICE 

Mr.  Norris  gives  a  table  of  capacity,  cost,  etc.,  for  two  of 
these  plants,  as  follows  : 

WATER    HOIST. 

Wm.  Penn  Mine.  Lyttle  Mine. 

Depth  of  shaft 953  feet.  1,500  feet. 

Capacity  of  tanks 1,440  gals.  2,600  gals." 

Size  of  engines 32  x  48  ins.  36  x  60  ins. 

Size  of  drums * Straight  12  ft.  diam.  Cone  10  to  16  ft. 

Capacity  of  hoist  in  24  hours. .. .     2,100,000  gals.  3,750,000  gals. 

Best  record,  24  hours 2,291,040  gals.  3,772,600  gals. 

COST,    SHAFT    AND    HOIST. 

Sinking  and  timbering $20,673.81  $22,641.63 

Head  frame    4,224.13  3,540.58 

Water  hoist,  engines  and  house.  .       15,583.64  29,653.17 

Tanks  and  ropes 2,393.23  3,899.65 

Steam  line 3,726.12  16,091.76 


$46,600.93  $80,777.96 

Cost  without  shaft  &  steam  plant.     $22,201.00  $37,093.40 

At  these  plants  Mr.  Norris  summarizes  the  operating-  cost 
of  hoisting  water  by  this  method  as  follows,  for  the  time  noted : 

Fidler  Mine,  Wm.  Penn  Mine,  Lyttle  Mine, 

3  years.  37  days.  i  month. 

Depth  of  shaft,  feet 960  953  1,500 

Water  hoisted,   gals 918,501,200         112,468,080  236,906,000 

Average  height  hoisted,  feet 960  727.8  740.6 

Cost   of   labor,    supplies   and    re- 
pairs per  1,000  gals $0.0114  $0.0088  $0.0071 

Cost  of  steam  per  1,000  gals.  ..  .          0.0192  0.0146  0.0148 


Total  cost  per  i,ooo  gals. . . .        $0.0306  $0.0234  $0.0219 

Estimating  on  the  above  data,  the  author  places  the  cost  of 
hoisting  water,  per  1,000  gallons  lifted  i,ooo.feet  vertically,  at 
$0.032,  $0.029  and  $0.028  respectively.  As  compared  with 
this  he  finds  that  the  average  cost  of  pumping  water  in  the 
collieries  of  the  Lykens  Valley  Coal  Company  is  $0.0533  and 
$0.0390  per  1,000  gallons  pumped  1,000  feet  vertically. 

Aside  from  any  actual  saving  in  operating  cost,  Mr.  Norris 
claims  that  there  are  other  decided  advantages  in  the  hoisting 
plan.  (i)  Simplicity  of  construction;  (2)  all  the  operating 
plant  is  on  the  surface,  with  a  resulting  low  cost  for  repairs ;  (3) 
there  is  an  almost  total  absence  of  slip ;  (4)  the  operating  plant 
cannot  be  flooded. 

An  automatic  electric  water-hoist  is  used  at  one  of  the 
anthracite  mines  of  the  Delaware.  Lackawanna  and  Western 


SOME  DATA   UPON   THE   COST   OF   TUNNELING  197 

Railroad.  This  hoist  lifts  4,000  gallons  of  water  per  minute 
through  a  height  of  550  feet.  Mr.  H.  M.  Warren,  the  elec- 
trical engineer  of  the  company,  specified  an  800  horse-power 
induction  motor  to  drive  the  hoist,  running  continuously  in  one 
direction,  fitted  with  reversing  clutches  for  driving  the  hoist- 
ing drum.  The  motor  drives  a  pair  of  bevel-gears  by  means  of 
a  single  bevel  pinion ;  and  the  bevel-gear  shaft  carries  a  pinion 
which  engages  the  main-gear  on  the  drum-shaft.  The  two 
drums  are  of  the  cylindro-conical  type,  16  feet  and  10  feet 
in  diameter.  A  steel  head-frame,  93  feet  high,  carries  two  steel 
two-inch  cables  terminating  in  two  steel  buckets,  each  6  feet  in 
diameter  and  19  feet  6  inches  long;  each  bucket  holding  17 
tons  of  water.  These  buckets  have  bottom  lift-gates  which 
open  automatically  when  the  buckets  reach  the  top  and  dis- 
charge the  water  through  two  lateral  spouts  into  concrete  basins 
built  on  either  side  of  the  shaft.  The  hoist  makes  a  complete 
round  trip  in  I  minute  50  seconds,  including  a  stop  at  either^ 
end  of  the  travel  long  enough  to  let  the  upper  bucket  empty. 

Cost  of  Square-set  Mine  Timbering. — In  1902  Mr.  Bernard 
Macdonald  presented  to  the  Canadian  Mining  Institute  a  paper 
on  "Mine  Timbering  by  the  Square-set  System  at  Rossland, 
B.  C."  From  this  the  following  data  are  taken  relating  to  cost : 

The  square^set  is  a  rectangular  skeleton  framework  of  posts, 
silk,  girts,  diagonal  braces  and  caps,  all  of  comparatively  short 
lengths  and  mortised  together.  Round,  peeled,  seasoned  logs, 
or  sawed  timber,  8  to  10  inches  in  diameter,  may  be  employed; 
though  in  the  Rossland  mine  1 6-inch  round  sticks,  16  feet  6 
inches  long,  were  also  used.  A  square-set,  including  one  post, 
one  cap,  and  a  girt  or  brace,  requires  18^  lineal  feet  of  logs, 
which,  at  8  cents  per  foot  in  this  case,  cost  $1.50  a  set  at  the 
framing  shed.  The  cost  of  framing  is  about  $0.55  per  set, 
framed  by  hand  labor  by  carpenters  receiving  $3.50  for  nine 
hours'  work.  The  detail  of  this  cost  is : 

For  material.  For  labor. 

One  post $0.65  $0.167 

One  cap   43  .219 

One  girt    40  .187 

Total $1.48  $0.573 


198  MODERN    TUNNEL    PRACTICE 

The  cost  per  set  in  place  is : 

Material   $1.48 

Labor  in  framing 57 

Lowering  into  mine,  about .10 

Delivering  at  place,  about 10 

Labor  erecting  1.50 

Wedges,  nails,  etc .10 

Sill  floor,  averaged  over  1 1   sets » .15 


Total  per  set,  about $4-00 

Segregating  the  labor  items,  we  find  that  one  set  of  i&J- 
lineal  feet  of  timber  costs  $2.27,  or  about  12  cents  per  lineal 
foot.  If  the  timbers  were  12x12  inches  the  labor  cost  would 
be  about  $10  per  1,000  feet,  board  measure,  which  is  not  ex- 
cessive, considering  the  high  rate  of  wages. 

Mr.  Macdonald  says  that  the  average  space  to  be  excavated 
for  each  set  is  5.3  feet  wide,  5  feet  long,  and  9  feet  high,  or 
240  cubic  feet.  Since  the  Rossland  ore  yields  200  pounds  per 
cubic  foot  in  place,  the  cost  of  timbering  amounts  to  17  cents 
per  ton  of  ore  mined. 

Mine  Hauling  by  Compressed  Air — Mr.  Richard  Hirsch,  in 
a  paper  upon  this  subject  read  before  the  Engineers'  Society  of 
Western  Pennsylvania,  gives  some  data  upon  the  cost  of  haul- 
ing in  mines  by  compressed  air  locomotives. 

The  30  mules  formerly  used  were  replaced  by  2  compressed- 
air  locomotives,  with  7x  1 4-inch  cylinders;  tank  capacity,  130 
cubic  feet;  tank  pressure,  500  pounds  per  square  inch.  They 
were  built  by  the  H.  K.  Porter  Company,  of  Pittsburg.  Each 
locomotive  weighed  16,000  pounds. 

In  1897  this  plant  was  operated  a  total  of  197  days  in  Col- 
liery No.  6  of  the  Susquehanna  Coal  Company,  at  Lyon,  Pa. 
The  contrasted  cost  of  operating  with  locomotives  and  mules  is 
summarized  below : 

Total  cost  of  plant,  except  steam  boilers,  cars  and  track $15,156.00 

Operating   expenses,    including    all    labor,    fuel,     supplies,    re- 
pairs, etc 2,202.78 

Fixed  charges,  including  interest,  depreciation  and  renewals...  1,776.60 

Cost  of  mules  required  for  same  work 4,052.48 

Cost  of  operation  by  mules,  including  labor,  supplies,  interest, 

depreciation,  etc.,  for  179  days 11,328.63 

Cost  of  operation  by  compressed  air 3,979-38 


Saving  in  cost  of  operation $7,349.25 


SOME  DATA   UPON   THE   COST   OF  TUNNELING  IQ9 

The  daily  average  work  of  these  two  motors  for  197  days 
was  1,185  net  ton-miles;  or,  the  cost  of  hauling  per  net-ton 
mile  was  1.9  cents.  The  corresponding  cost  by  mule  haulage 
was  5.34  cents.  For  300  working  days  the  contrast  would 
have  been  still  greater. 

Cost  of  Diamond-drill  Exploration  in  South  Africa — The  1901 
report  of  the  Commissioner  of  Mines  for  Natal  Colony,  South 
Africa,  gives  some  interesting  data  as  to  the  cost  of  explor- 
ing by  the  diamond  drill  in  that  country. 

The  carbons  used  were  inferior  Brazilian  diamonds,  costing 
$50  per  carat,  and  Kimberly  stones  at  $15  per  carat.  The  cost 
of  the  carbons  per  foot  of  hole  drilled  was  20  cents  for  a  2.\- 
inch  hole  in  the  softer  rock,  and  $1.35  for  a  3-inch  hole  in 
quartzite.  Both  hand-driven  and  steam  drills  were  used. 

With  hand-driven  drills,  the  cost  and  progress  made  is  shown 
by  the  following  table : 


I. 

2. 

3- 
4- 

6. 
8." 

Sandstone. 
Sandstone. 
Shale. 
Sandstone. 
Sandstone. 
Whinstone. 
Sandstone. 
Shale. 

2 
2 
2 
2 
2 
2 
3 

3 

78 
80 
28  • 

161 
34i 
369 
8l 
116 

9 
9 
3 

35 

93^ 
7 

8.7 
8.9 
9-5 
ii.  i 
9-7 

11.6 
7.8 

$145-54 
142.15 

48.95 
464.55 
406.35 
2,146.00 
197.65 
240.60 

$1.86 

2.02 
1.70 
2.90 
1.20 
5-85 
2.44 
2.IO 

2 
IO 

5 

12 
0 

o 

6 
i 

For  drills  driven  by  steam  power,  the  similar  record  for  an- 
other set  of  holes  is  as  follows : 


^  c  %  I  ?  i 

S  ">  -si  *>"  2  *»  ^  -^  ° 

^                     "^                    ~  ~  <^H«;  >^-§  •**  **  •*»  •*» 

-5                                     £                                 '^    =•  Q    *  "^    O  ^<S  L?  ^  ^ 

1.  Shale.                         6  170  24  7.1  $401.70  $2.34  2 

2.  Shale.                         3  96  5^  17.5  267.40  2.79  30 

3.  305  ft.  Shale. 

146  ft.  Whinst'e.      3  615  77^  7.9  1,851.25  3.40  4 

4.  Sandstone.                 2^  85  2^  18.9  145-35  I-7O  — 

5.  Sandstone.                 2^  176  3^  25.4  165.40  0.92  o 

6.  Sandstone.                 2^  147  2^  34.7  154.50  1.05  9 
7-       Sandstone.                 2^2  201  5^  36.5  153.00  0.76  15 
8.       Sandstone.                6  154  17^  5.8  1,181.70  7.55  13 


2OO  MODERN    TUNNEL    PRACTICE 

In  both  tables  only  the  actual  boring  shifts  are  noted ;  about 
20%  of  the  actual  time  consumed  and  paid,  for  in  total  cost 
was  taken  up  by  Sundays  and  holidays.  On  a  steam  drill  the 
crew  numbered  i  white  man  and  5  to  6  natives,  and  the  wages 
paid  were  evidently  very  low,  amounting  to  about  $4.50  pel- 
drill  crew,  including  rations.  On  hand-drills  I  white  man  and 
8  natives  were  employed. 

Cost  of  Diamond-drill  Work  in  Montana Mr.  A.  P.  Davis, 

Principal  Engineer  U.  S.  Geological  Survey,  gives  the  follow- 
ing data  on  diamond-drill  boring  in  connection  with  the  irri- 
gation surveys  in  Montana.* 

Six  holes  were  bored  to  an  aggregate  depth  of  340  feet,  a 
hard,  somewhat  coarse  and  seamy  granite  being  generally 
found  about  40  to  50  feet  below  the  surface  of  the  rivers  in- 
vestigated. The  total  expenditure  for  the  gang  of  4  to  5  men 
was  $523  per  month,  including  salaries  ($330),  subsistence, 
interest  at  3%  on  machinery  costing  $2,800,  wear  and  loss  of 
carbons  ($30),  and  fuel. 

At  26  working  days  (of  10  hours  each)  to  a  month,  it  cost 
$20.12  per  working  day  to  run  the  drill.  It  took  38^  working 
days  to  put  down  the  6  holes,  at  a  total  cost  of  $769.60.  As 
the  combined  depth  of  the  holes  was  340  feet,  this  averages 
$2.26  per  foot  of  holes  drilled.  But  of  this  340  feet  only  79 
feet  was  diamond-drilling,  and  55  feet  was  water. 
^Engineering  News,  April  30,  1903. 


CHAPTER    XI 

THE  VENTILATION    OF   TUNNELS 

The  principles  of  artificial  ventilation — The  Saccardo  system — Ventilation 
methods  on  the  Boston  Subway — The  East  Boston  tunnel — The  Balti- 
more &  Potomac  tunnel — The  Paris-Orleans  Railway — The  Penn- 
sylvania Avenue  Subway  in  Philadelphia — The  Simplon  tunnel. 

The  mechanical  ventilation  of  a  tunnel,  whether  in  process 
of  construction  or  in  actual  operation,  is  one  of  the  trouble- 
some problems  presented  to  the  engineer.  In  the  one  case, 
the  fumes  arising  from  the  blasting  charges  have,  to  be  re- 
moved as  speedily  as  possible  from  the  headings,  so  as  to  avoid 
loss  of  time  in  clearing  away  the  broken  rock ;  and,  in  the  other 
case,  the  air  vitiated  by  the  gases  arising  from  the  combustion 
of  coal  has  to  be  replaced  by  fresh  air. 

In  tunnel  construction  the  heading  is  usually  cleared  by  lead- 
ing: a  tight  but  light  pipe  as  near  to  the  heading  as  possible, 
and  then  sucking  or  blowing  out  the  foul  air  by  a  fan  of  suit- 
able dimensions,  located  at  the  portal  or  on  top  of  a  shaft.  In 
ordinary  operations,  the  working  conditions  are  such  that  more 
elaborate  appliances  are  not  economical. 

In  a  railway  tunnel,  with  a  dense  traffic  through  it,  ventila- 
tion is  a  more  serious  problem.  In  certain  cases,  where  the 
ratio  of  the  necessary  interval  between  trains  to  the  velocity 
of  the  natural  current  through  the  tunnel  is  not  too  great,  nat- 
ural ventilation  may  clear  the  tunnel  of  foul  air.  The  natural 
current  here  referred  to  is  dependent  upon  the  difference  in 
temperature  inside  the  tunnel  and  outside,  and  upon  the  dif- 
ference in.  barometric  pressure  between  the  two  portals — in 
other  words,  their  relative  elevation  above  sea  level.  In  small 
tunnels  these  two  causes  are  not  appreciably  operative;  but 

201 


2O2  MODERN     TUNNEL    PRACTICE 

wind  action  and  the  mechanical  effect  of  the  train  passing 
through  a  tube  may  effect  the  ventilation. 

Artificial  ventilation  is  now  the  rule  wherever  the  train  in- 
tervals are  short;  and  the  principle  generally  adopted  is  that 
of  exhausting  the  vitiated  air  at  a  point  midway  of  a  tunnel, 
or  tunnel  section,  and  drawing  in  fresh  air  at  the  ends  of  the 
section. 

In  a  paper  upon  this  subject,  presented  to  the  Institution 
of  Civil  Engineers  by  Francis  Fox,  M.  Inst.  C.  E.,  the  author 
says  that  he  has  ascertained  by  experiment  that  so  long  as  the 
amount  of  carbon  dioxide  in  the  air  does  not  exceed  20  parts 
in  10,000,  the  air  in  a  railway  tunnel  is -satisfactory. 

Mr.  Fox  goes  on  to  say  that,  having  ascertained  the  consump- 
tion of  coal  by  a  locomotive  in  its  passage  through  a  tun- 
nel, and  allowing  29  cubic  feet  of  poisonous  gases  for  each 
pound  of  coal  consumed,  the  volume  of  fresh  air  required  to 
maintain  the  tunnel  at  the  above  standard  can  be  ascertained 
as  follows : 

The  number  of  pounds  of  fuel  consumed  per  mile,  multiplied 
by  29,  multiplied  by  500,  and  divided  by  the  number  of  min- 
utes' interval  between  trains,  will  give  the  cubic  feet  of  air 
which  must  be  introduced  per  minute  into  the  tunnel.  Assum- 
ing as  an  illustration  a  tunnel  one  mile  long,  consumption  of 
fuel  32  pounds  per  mile,  and  one  train  passing  through  the 
tunnel  in  each  direction  every  five  minutes,  the  volume  of  fresh 
air  required  per  minute  will  be : 

32  Ibs.  X  29  cu.  ft.  X  500 

_  =  185,600  cu.  ft. 

2.\  mm. 

This  is  the  basic  principle  of  the  ventilation  of  the  Mersey 
and  Severn  tunnels;  and  the  ventilation  was  satisfactory  until 
the  traffic  exceeded  the  capacity  of  the  ventilating  plant  origi- 
nally put  in.  In  the  Mersey  tunnel  the  system  of  electric  trac- 
tion was  adopted  in  1902. 

Experience  in  the  operation  of  city  subways  by  electric  power 
tends  to  prove  that  ventilating  appliances,  especially  in  summer, 


THE    VENTILATION    OF    TUNNELS  203 

are  almost  as  necessary  as  in  the  older  tunnels.  In  this  case, 
however,  it  is  a  question  of  reducing-  undue  heat  rather  than 
that  of  the  removal  of  gases  resulting  from  the  combustion  of 
coal. 

In  these  electrically  operated  underground  tunnels  we  have 
a  great  number  of  motors  constantly  consuming  a  very  large 
quantity  of  electric  power.  This  power  is  almost  wholly  ex- 
pended in  overcoming  friction  in  the  journals,  in  the  wheels 
and  rails,  in  brake-shoes,  and  in  the  air  at  the  head  and  sides 
of  trains;,  and  even  the  force  used  to  overcome  the  inertia 
of  the  trains  is  expended  again  in  friction  when  the  brakes 
are  set  to  retard  the  trains;  and  the  electricity  lost  in.  trans- 
mission through  the  third  rail  is  a  frictional  loss.  This  ex- 
pended power  is  not  lost;  it  is  converted  into  heat,  and  this 
addition  to  normal  temperature  must  be  reckoned  with  by  the 
engineer  designing  subways. 

Actual  experiments  made  in  the  New  York  subways  in  the 
summer  of  1905  show  that  the  temperature  in  the  subway  and 
in  the  cars  is  from  4°  to  6°  higher  than  the  thermometric  read- 
ings taken  at  the  same  time  at  the  street  surface  above.  These 
New  York  subways  exceed  any  previously  operated  subway  in 
the  traffic  density,  weight  of  trains,  size  of  motors,  and  power 
expended.  And,  while  complaints  have  been  made  of  bad  venti- 
lation in  some  of  the  earlier  electric-motor  operated  tunnels, 
it  has  remained  for  the  New  York  subway  to  demonstrate  that 
the  heating  effect  of  electric  power  upon  the  air  of  the  sub- 
way must  be  considered  and  provided  for  in  the  design  of 
such  tunnels. 

In  designing  the  Boston  subway,  also  operated  by  electricity, 
the  engineers  provided  an  efficient  ventilation  plant,  described 
later  in  this  chapter.  But  while  this  plant  was  originally  em- 
ployed to  regulate  the  temperature  within  the  tunnel  and  to 
prevent  it  from  falling  to  a  point  too  much  below  the  normal 
temperature,  it  has  certainly  regulated  as  well  the  surplus  heat 
in  that  tunnel  resulting  from  the  expenditure  of  electric  power. 
This  tunnel  is  cool  in  summer,  though  it  cannot  compare  in 
traffic  and  in  motor  power  with  the  New  York  subways. 


2O4 


MODERN    TUNNEL    PRACTICE 


Saccardo  System  of  Ventilation — The  Pracchia  tunnel  is  one 
of  52  single-track  tunnels  on  the  railway  between  Florence  and 
Bologna,  in  Italy.  The  gradients  are  about  i  in  40,  and  the 
traffic  requires  the  use  of  heavy  locomotives.  The  Pracchia 
tunnel  is  9,000  feet  long;  under  any  condition  of  wind  the  air 
within  is  bad,  and  with  a  wind  blowing  in  at  the  lower  end  the 
state  of  affairs  is  almost  insupportable. 

Marco  Saccardo,  a  prominent  Italian  engineer,  applied  his 
system  of  ventilation  to  this  tunnel  with  remarkable  results. 
He  availed  himself  of  the  annular  space  between  the  interior 
of  the  tunnel  and  the  extreme  cross-section  of  the  carriage. 
And,  upon  the  principle  of  the  injector,  he  uses  a  fan  to  blow  a 
large  volume  of  air  into  the  mouth  of  the  tunnel :  this  induces  a 


Plan 

FIG.   101. — The  Saccardo  System  of  Tunnel  Ventilation. 

strong  inward  current  through  the  central  opening  used  by 
the  train. 

As  shown  in  Fig.  101,  Saccardo  extended  the  tunnel  by  a 
structure  of  brick,  about  20  feet  long;  the  inside  of  the  central 
opening  representing  the  line  of  maximum  train  cross-section. 
This  structure  extended  about  3  feet  into  the  tunnel,  with  an 
opening  toward  the  tunnel  through  which  air  was  forced  from 
the  air-chamber. 

Francis  Fox,  M.  Inst.  C.E.,  measured  the  volume  and  tem- 
perature in  the  tunnel  thus  equipped,  with  the  following  result : 
Before  starting  the  fan  the  tunnel  was  rilled  with  dense  smoke 


THE   VENTILATION    OF    TUNNELS  2O5 

from  end  to  end;  the  temperature  was  107°  F.,  with  97°  of 
moisture,  or  nearly  complete  saturation.  With  the  fan  running 
the  temperature  fell  to  80°,  or  that  of  the  external  air ;  the  mois- 
ture was  normal;  the  amount  of  air  propelled  by  the  fan  was 
164,000  cubic  feet  per  minute,  with  46,000  cubic  feet  resulting 
from  the  induced  current,  making  a  total  of  210,000  cubic  feet 
of  air  per  minute  passing  through  the  tunnel.  The  air  was 
blown  in  at  the  upper  end  of  the  tunnel;  with  the  object  that 
the  gases  from  an  ascending  train  may  be  blown  down  the  in- 
cline and  out  at  the  lower  end.  Mr.  Fox  says  that  the  air  in 
the  tunnel  was  cool  and  fresh.  But  this  principle  could  not  be 
applied  to  subways,  as  the  smoke  would  simply  be  blown  to  the 
next  station,  just  where  everything  should  be  clear. 

Boston  Subway — While  this  subway  is  operated  by  electric- 


/• 


FIG.  102. — Ventilating  Chamber :   Boston   Subway. 

ity,  and  the  removal  of  smoke  and  gases  resulting  from  the 
combustion  of  coal  need  not  be  considered,  engineers  now  rec- 
ognize the  necessity  of  a  positive  and  continuous  change  of  air 
in  subways.  This  is  necessary  for  the  double  purpose  of  main- 
taining the  purity  of  the  air  and  for  regulating  the  moisture 
in  the  air,  thus  preventing  the  deposit  of  moisture  and  the 
chilling  of  passengers  and  employes.  The  dew-point  of  air 
of  90°  F.,  with  a  relative  humidity  of  70%,  is  about  79°  F.  It 
is  thus  plain  that  with  an  external  temperature  of  90°,  and  a 
slow  and  uncertain  movement  in  the  air  within  the  tunnel,  this 
air  may  be  readily  cooled  through  10°  or  more;  it  would  then 
become  saturated,  cause  inconvenience  by  drippings  from  the 
structural  work,  and  become  a  positive  menace  to  health. 


206  MODERN     TUNNEL    PRACTICE 

For  these  reasons  the  plans  for  the  Boston  subway  called 
for  ventilating  stations  located  at  suitable  points  and  equipped 
with  fans  driven  by  electric  motors.  These  stations  are  placed 
about  midway  between  entrances;  and  the  fans  are  designed 
to  change  the  air  in  any  one  section  once  in  15  minutes. 

Fig.  1 02  shows  the  general  design  of  one  of  these  stations. 
All  of  the  fans  are  of  the  Sturtevant  cone  type,  and  the  two 
fans  between  Hollis  and  Eliot  streets  are  each  7  feet  in  diameter 
and  are  each  designed  to  deliver  30,000  cubic  feet  of  air  per 
minute,  at  175  revolutions  per  minute;  they  require  an  expen- 
diture of  about  7  horse-power  each  under  ordinary  conditions. 
Each  fan  is  provided  with  an  electric  motor  directly  connected 
to  the  fan-shaft  by  an  insulated  coupling,  and  mounted  on  a 
substantial  insulating  base-frame  made  of  Georgia  pine,  thor- 
oughly filled  to  prevent  absorption  of  moisture. 

East  Boston  Tunnel — In  the  harbor  portion  of  this  tunnel, 
which  is  to  be  operated  by  electric  cars,  a  complete  ventilation 
system  has  been  installed  on  the  following  plan :  The  double- 
track  tunnel  under  the  harbor  is  about  23^  feet  wide  at  the 
springing  line  of  the  arch,  with 'a  cross-section  of  332  square 
feet ;  while  the  four-track  land  sections  have  a  cross-section  of 
707  square  feet.  In  both  land  and  harbor  sections  resort  is  had 
to  direct  ventilation  by  exhaust  fans;  the  exhaust  fans  being 
set  in  chambers  about  midway  between  stations.  These  fans 
take  the  air  from  the  tunnel  and  discharge  it  upward,  usually 
through  grated  openings  in  the  sidewalks.  Fresh  air  enters 
at  the  stations  and  flows  each  way  to  the  fans. 

The  harbor  section  is  provided  with  a  shaft  at  either  end 
containing  the  exhaust  fans,  located  near  the  surface.  In  the 
crown  of  the  tunnel  is  a  duct,  with  a  cross-section  of  48  square 
feet,  this  duct  being  made  of  a  diaphragm  i  inch  thick,  con- 
structed of  expanded  metal  and  concrete.  This  diaphragm  is 
suspended  to  the  crown  of  the  arch  by  steel  rods  and  plates  also 
incased  in  concrete.  Midway  of  the  tunnel  a  partition  divides 
this  duct  into  two  parts,  and  on  each  side  of  this  partition  there 
are  14  openings,  each  4  feet  long  and  i  foot  5  inches  wide,  sit- 
uated in  the  flat  portion  of  the  duct ;  and  at  intervals  of  about 


THE    VENTILATION    OF    TUNNELS  2O7 

550  feet  there  are  other  groups  of  openings,  diminishing  in 
number  as  they  approach  the  fan  chambers.  These  openings 
are  fitted  with  doors  that  can  be  operated  from  the  tunnel  below. 
When  the  movement  of  the  air  in  the  tunnel  is  not  effected  by 
the  wind  the  two  groups  of  openings  close  to  the  middle  parti- 
tion are  alone  used. 

Fresh  air  enters  the  tunnel  at  the  portal  at  East  Boston  and 
through  the  station  at  Atlantic  avenue  on  the  Boston  side.  This 
fresh  air  from  both  ends  passes  to  near  the  middle  of  the  tunnel 
and  is  drawn  into  the  openings  near  the  middle  portion  by  the 
action  of  the  exhaust  fans,  and  is  discharged  through  the  ven- 
tilation ducts  and  through  the  fan-shafts  at  either  end. 

It  should  be  mentioned  that  the  ventilating  duct  is  curved 
downward  for  the  central  two-thirds  of  its  entire  span,  or  be- 
tween the  suspending  rods  and  plates.  The  two  side  portions, 
between  the  suspenders  and  the  arch,  are  flat,  and  in  these  the 
openings  referred  to  are  located. 

Baltimore  &  Potomac  Tunnel — The  ventilating  plant  here 
described  is  found  in  the  tunnel  of  the  Pennsylvania  Railroad 
Company,  in  the  city  of  Baltimore,  built  in  1892,  under  Joseph 
T.  Richards,  Assistant  Chief  Engineer  Pennsylvania  Railroad 
Company.  This  plant  was  one  of  the  first  of  its  type  to  be 
operated  by  electric  power. 

The  plant  includes  a  motor-house,  a  stack  102  feet  high  and 
13  feet  6  inches  square  inside,  and  the  conduit  connecting  the 
tunnel  with  the  fan-chamber.  The  fan  is  a  plain  Davidson 
ventilating  wheel,  15  feet  in  diameter,  with  a  velocity  of  658 
feet  per  minute  at  the  periphery.  The  conduit  is  circular,  15 
feet  6  inches  diameter.  This  plant  controls  3,600  feet  of 
tunnel  measured  between  portals,  and  it  is  designed  to  change 
the  air  in  the  tunnel  once  in  five  minutes;  this  requiring  a 
velocity  of  4-2.6  feet  per  second  in  the  air  passing  through  the 
conduit  connecting  the  tunnel  and  the  shaft. 

The  power-house  is  located  about  3,200  feet  distant  from  the 
fan-chamber,  and  it  contains  a  100  horse-power  boiler,  a  90 
horse-power  engine,  and  an  80  horse-power  Thomson-Houston 
dynamo.  A  copper  cable  transmits  the  power  to  the  motor- 


208 


MODERN    TUNNEL    PRACTICE 


house,  which  contains  a  45  horse-power  Thomson- Houston 
motor,  which  is  so  connected  as  to  run  the  fan  at  14  revolutions 
per  minute. 

Paris-Orleans  Railway — The  Paris  section  of  this  tunnel  is 
operated  by  steam  locomotives,  as  it  was  deemed  inadvisable 
to  change  the  traction  system.  As  a  result,  mechanical  ventila- 
tion was  introduced. 

The  plan  adopted  was  very  similar  to  that  used  at  the  Mersey 
tunnel,  as  shown  in  Fig.  104.  Just  outside  the  haunch  of  the 
main  arch  a  small  circular  conduit  was  built,  connected  with  a 


•- 
% .-'  Filling  up  tv  Paving  of  Street 

33'0--- * 

-* 141.0      p    Wilson  St. I 


Section-G-D,    ^ 

Center  Lw   of 

FIG.  103.— Baltimore  &  Potomac  Tunnel:   Section  of  Conduit  Leading  to 

Fan-chamber. 

fan  at  the  main  station.  This  conduit  connected  with  the  tunnel 
at  regular  intervals ;  and  fresh  air  was  taken  into  the  tunnel 
through  the  stations,  and  also  through  specially  provided  inlets 
in  the  sidewalks,  covered  by  a  small  building  with  the  sides 
used  for  advertising  purposes.  The  system  seems  to  work 
well. 

Pennsylvania  Avenue  Subway — This  subway,  about  3,000 
feet  long,  was  built  by  the  Philadelphia  &  Reading  Railroad 
Company  to  remove  17  dangerous  grade  crossings  in  the  heart 
of  Philadelphia.  The  tunnel  section  has  the  unusual  dimen- 
sions of  52  feet  span  in  the  clear  and  it  is  22  feet  high.  As  the 
traffic  is  dense  a  complete  system  of  artificial  ventilation  had  to 
be  provided  for. 

The  general  plan  is  shown  in  Fig.   1043,  and  includes  two 


THE    VENTILATION    OF    TUNNELS  2OQ 

fan  stations,  side  exhaust  conduits  and  fresh-air  intakes.  The 
two  fan  stations  divide  the  tunnel  into  four  almost  equal  sec- 
tions. At  each  station  are  two  2O-foot  fans  driven  by  electric- 
ity, which  draw  out  the  foul  air  through  openings  in  the  arch 
located  at  150- foot  intervals;  these  openings  lead  to  a  circular 
conduit  of  varying  dimensions,  draining  toward  the  fan  sta- 
tions. The  conduits  decrease  in  diameter  from  n  feet  at  the 
fan  station  to  6|  feet  at  the  ends. 

The  fresh-air  intakes  are  located  on  the  other  side  of  the 
tunnel  and  deliver  the  air  at  the  rail-level.     These  intakes  are 


Ventilation, 
Heading, 


Cross  Section. 
FIG.  104. — Mersey  Tunnel :  Showing  Ventilating  Conduit. 

located  midway  between  the  foul-air  openings  and,  as  a  rule, 
they  are  placed  in  grass  plots  falling  between  the  curb  and  the 
sidewalk. 

Each  fan  is  figured  to  have  a  capacity  of  150,000  cubic  feet 
per  minute,  or  600,000  cubic  feet  in  all ;  as  this  is  about  one- 
fifth  of  the  cubic  contents  of  the  tunnel,  the  air  should  be  re- 
newed every  5  minutes. 

Ventilation  of  the  Simplon  Tunnel. — -For  ventilating  this  tun- 
nel during  and  after  construction  a  permanent  ventilating  plant 
was  installed  at  each  end  of  its  12.4  miles  length.  The  plant 
at  each  end  consisted  of  two  200  horse-power  turbines  running 
at  400  revolutions  per  minute  and  driving  two  fans,  each  12.3 
feet  in  diameter.  The  elevation  of  the  Swiss  entrance  to  the 


210 


MODERN    TUNNEL    PRACTICE 


tunnel  is  2,250  feet  above  sea  level,  while  the  elevation  at  Iselle, 
at  the  Italian  end,  is  2,076  feet  above  the  same  level.  The  high- 
est point  of  the  tunnel,  about  midway,  has  an  elevation  of  2,310 
feet  above  sea  level. 

At  the  Swiss  end  the  fans  were  placed  one  above  the  other, 
close  to  the  portal ;  and  at  the  Italian  end  the  fans  were  placed 
one  behind  the  other.  In  the  latter  case  the  air  passes  first  to 
a  ventilator-house,  and  thence  by  a  passageway  to  the  tunnel. 
The  ventilating  plant  at  each  end  furnished  50  cu.  m.  of  air  per 
second  at  a  gage  pressure  of  25omm.  of  water,  when  running 
in  parallel;  and  25  cu.  m.,  at  a  pressure  of  500  mm.  of  water, 


•"RocA Section 

FIG.  iO4a. — Ventilation  of  the  Pennsylvania  Avenue  Subway. 

when  running  in  series  in  a  tunnel  10  kilos  long  and  8  square 
metres  in  sectional  area. 

It  should  be  stated  that  two  twin  tunnels  form  this  line,  each 
single-track,  spaced  55.76  feet  apart,  c.  to  c.  These  tunnels 
are  lined  throughout  with  masonry;  and  though  the  thickness 
of  the  lining  varies,  the  clear  width  of  each  tunnel  at  the  spring- 
ing line  is  16.43  ^eet-  During  construction  only  one  of  the 
tunnels  was  driven  to  its  full  dimensions,  the  other  being  rep- 
resented by  a  small  gallery  which  served  for  drainage,  ventila- 
tion and  other  purposes  connected  with  the  tunnel  work.  At 
intervals  of  656  feet  the  tunnel  and  this  service  gallery  were 
connected  by  transverse  galleries  laid  out  on  an  angle  of  about 
60°  with  the  tunnel  axis.  The  alignment  of  the  tunnel  is 
straight,  except  for  a  short  curve  at  each  end. 


THE    VENTILATION    OF    TUNNELS  211 

Returning  to  the  ventilating  plant,  the  air-passage  from  the 
ventilator-house  bifurcates  near  its  tunnel  end  and  one  fork  goes 
to  each  tunnel ;  a  door  at  the  angle  of  the  bifurcation  closes 
either  passage  to  the  tunnels  at  will.  Sailcloth  curtains  close 
the  portals  of  the  tunnel,  and  these  are  operated  by  hand  or  15y 
electric  motors.  By  this  arrangement — and  when  the  tunnels 
are  completed — the  air  can  be  circulated  in  either  tunnel  as 
desired,  the  movement  of  the  air  being  accomplished  by  com- 
pression or  by  aspiration;  the  cross-galleries  between  the  tun- 
nels referred  to  having  been  then  sealed  up. 

To  ventilate  the  workings  during  construction  was  a  more 
complicated  operation.  In  this  case  the  air  was  forced  through 
a  branch  to  the  service  gallery,  and  it  passed  along  this  gallery 
to  the  most  advanced  cross-gallery,  and  then  back  to  the  portal 
along  the  main  tunnel  of  full  section.  If  the  air  were  exhausted 
instead  of  being  forced  in,  the  direction  of  flow  would  be  in  the 
opposite  direction.  It  should  also  be  noted  that  all  side  pass- 
ages are  sealed  up  as  the  work  advances  to  prevent  the  short- 
circuiting  of  the  air-current.  As  installed,  this  ventilating  plant 
was  in  excess  of  the  needs  of  construction.  One  fan  operating 
so  as  to  give  a  gage  pressure  of  6omm.  of  water,  gave  one 
cubic  foot  of  air  per  second  at  the  working  face.  An  increase 
of  pressure  to  loomm.  of  water  blew  out  the  miners'  lamps.  To 
lay  the  dust  and  freshen  the  air  entering  the  fans  the  sides  of  the 
air  passages  were  occasionally  flooded  with  water.* 

Before  commencing  this  work  the  elevation  of  temperature 
due  to  the  heat  of  the  rock  was  estimated  at  i°C.  for  every  4/jm. 
of  advance.  But,  owing  to  different  influences  encountered  the 
actual  temperatures  differed  materially  from  the  estimates.  At 
the  Italian  side  the  heavy  inflow  of  water  kept  the  air  cool  for 
a  considerable  advance.  But  on  the  Swiss  side  the  infiltration 
of  water  was  small  and  it  was  a  matter  of  some  difficulty  to 
keep  the  air  cool  enough  for  the  men  to  work.  The  highest 
temperature  met  with  up  to  the  autumn  of  1902  was  55°C, 
and  at  the  eighth  kilometer  from  the  Swiss  end. 

*A  detailed  description  of  the  plant  and  the  methods  pursued  in  driving 
the  Simplon  tunnel  will  be  found  in  Engineering  News  for  August,  1903. 


212  MODERN    TUNNEL    PRACTICE 

To  refrigerate  the  air,  cold  water  was  forced  into  the  head- 
ings and  then  broken  into  spray.  The  lo-inch  pipe  carrying  in. 
the  water  from  the  Rhone,  on  the  Swiss  end,  was  jacketed  with 
a  I5|-inch  pipe  and  the  annular  space  was  filled  with  charcoal. 
In  passing  through  9  kilometers  of  this  protected  pipe  the  rise 
in  temperature  in  the  water  was  only  3°C. 


CHAPTER  XII 

AIR-LOCKS 

The  general  purpose  of  air-locks  in  tunnel  work — Their  location — The 
limit  of  human  endurance  under  compressed  air — Effect  of  compressed 
air  upon  the  workmen — Compressed-air  hospital  locks — The  O'Rourke 
air-lock — Mirabeau  bridge  air-lock — The  Hughes  air-lock — Hyde  Park 
tunnel  air-lock — Morison  air-lock — Victoria  bridge  air-lock — Air- 
locks at  Kiel  dry-dock. 

So  far  as  tunneling  is  concerned,  compressed  air  is  only  em- 
ployed in  subaqueous  work,  located  not  more  than  about  100 
feet  below  the  water  surface.  Air-locks — the  essential  feature 
of  this  method  of  tunneling — cannot,  therefore,  be  omitted  in 
this  work,  as  shaft-sinking  is  a  form  of  vertical  tunneling; 
and  when  much  water  is  encountered,  compressed  air  is  com- 
monly used  for  its  expulsion.  This  chapter  on  air-locks  has 
been  made  quite  general  in  its  application. 

Briefly  expressed,  an  air-lock  is  a  means  devised  by  engineers 
for  passing  from  the  outer  air  to  a  working  chamber  filled  with 
air  compressed  to  a  degree  sufficient  to  expel  and  support  the 
column  of  water  under  which  the  work  is  being  conducted.  As 
it  enables  the  workmen  to  pass  at  will  from  one  air-pressure  to 
another,  it  is  comparable  to  the  lock  of  a  canal  employed  for 
the  purpose  of  transferring  boats  from  one  water  level  to 
another. 

Air-locks  may  be  applied  vertically,  as  in  sinking  a  vertical, 
cylindrical  shaft  or  a  caisson;  or,  they  may  be  used  horizon- 
tally, as  in  subaqueous  tunneling  where  an  inrush  of  water  is 
to  be  guarded  against.  The  latter  use  of  air-locks  is  attended 
with  danger;  especially  if  the  soil  penetrated  is  sand  or  silt  with 
a  comparatively  slight  depth  of  material  between  the  roof  of  the 
tunnel  and  the  bed  of  the  river.  In  such  cases,  the  compressed 

213 


214  MODERN    TUNNEL    PRACTICE 

air  may  find  an  opening  in  this  loose  material;  and  a  "blow- 
out" occurs,  reducing  the  pressure  in  the  tunnel  so  suddenly 
that  an  inflow  of  water  may  result.  This  accident  occurred 
several  times  during  the  construction  of  the  North  River  tun- 
nel, through  silt,  and  in  one  case  many  lives  were  lost.  This 
contingency  is  often  guarded  against  by  the  use  of  clay-bags 
disposed  in  a  sufficiently  broad  layer  on  the  bed  of  the  river 
and  immediately  over  the  line  of  the  tunnel.  The  clay-bags 
are  better  than  loose  clay  deposited  on  the  river  bed,  as  the 
loose,  clay  may  be  washed  away  by  the  current. 

In  horizontal  tunneling,  double  sets  of  air-locks  are  usually 
provided;  one  set  devoted  exclusively  to  the  passing  out  of 
debris  and  the  passing  in  of  the  materials  of  construction,  and 
the  other  is  for  the  use  of  the  workmen.  In  work  of  this  char- 
acter it  is  also  customary  to  provide  guard-locks  to  prevent  the 
whole  length  of  a  tunnel  from  being  flooded  by  reason  of  any 
accident  to  the  main  advance  air-lock.  These  guard-locks  are 
usually  located  in  bulkheads  of  masonry  built  at  some  distance 
in  the  rear  of  the  advance  shield  and  lock,  and  thus  inside  the 
completed  lining  of  the  tunnel. 

In  the  horizontal  as  well  as  in  the  vertical  application  of 
compressed  air  to  structural  purposes,  by  means  of  air-locks, 
the  safety  of  the  workmen  demands  that  a  proper  time  should 
be  allowed  in  the  equalization  of  the  air-pressure  in  the  lock ; 
this  time  depending  upon  the  position  of  the  lock,  or  the  work- 
ing chamber,  in  relation,  to  the  water  surface,  and  the  conse- 
quent air-pressure  necessary  to  expel  the  water. 

The  chief  danger  lies  in  the  effect  upon  the  human  organism 
of  a  too  sudden  transition  from  a  high  air-pressure  to  the  nor- 
mal atmospheric  pressure;  though  evil  results  may  also  follow 
from  the  locking-in  process,  if  the  higher  pressure  is  too  quickly 
admitted  into  the  air-lock. 

A  series  of  interesting  experiments  were  made  in  1895,  by 
Mr.  Hersent,  the  engineer  of  the  harbor  works  at  Bordeaux,  as 
to  the  limits  of  human  endurance  under  higher  pressures  than 
those  usually  employed  in  the  pneumatic  process.  He  fitted  up 
a  test  air-lock  with  windows,  telephone,  electric  light,  steam 


AIR-LOCKS  215 

coil  for  heating,  etc.  Three  volunteers,  two  experienced  work- 
men and  one  who  had  only  been  under  air-pressure  a  few  times, 
were  subjected  to  pressures  for  about  one  hour  at  a  time.  The 
tests  commenced  with  a  pressure  of  about  28.4  pounds  per 
square  inch,  and  this  pressure  was  increased  very  gradually,  By 
about  4.27  pounds  per  day,  to  76.8  pounds  per  square  inch. 
The  time  for  the  pressure  reduction  was  increased  about  10 
minutes  for  each  1.42  pounds  in  increase  of  pressure.  All 
three  men  sustained  without  difficulty  a  pressure  of  46.9 
pounds,  with  a  reduction  period  of  56  minutes.  One  man  then, 
withdrew  from  the  test,  owing  to  an  independent  cause.  At 
58.3  pounds  pressure  the  man  accustomed  to  the  work  felt 
some  inconvenience;  and  at  65.4  pounds  the  man  who  was  not 
accustomed  to  compressed  air  had  to  be  withdrawn  as  he  suf- 
fered from  pain  in  his  side,  though  there  was  no  trace  of  par- 
alysis. But  the  experienced  man  withstood  a  pressure  of  71.1 
pounds  for  one  hour,  and  this  pressure  was  reduced  in  2  hours 
25  minutes.  This  same  man  underwent  the  final  test  of  a  pres- 
sure of  76.8  pounds,  raised  in  45  minutes  and  continued  for 
one  hour;  this  pressure  was  then  reduced  to  normal  pressure 
in  3  hours  3  minutes.  Mr.  Hersent  says  that  the  man  who 
endured  this  abnormal  pressure  suffered  no  inconvenience  other 
than  a  tingling  sensation,  which  passed  away  after  a  short 
time. 

Mr.  Hersent  believed  that,  if  certain  precautions  were  taken, 
men  in  good  health  could  safely  withstand  a  pressure  of  76.8 
pounds  per  square  inch  for  a  limited  time.  This  pressure  of 
76.8  pounds  is  equivalent  to  a  depth  of  about  178  feet  below  the 
water  surface  and  far  exceeds  any  depth  worked  under  com- 
pressed air.  For  a  long  time  about  100  feet  was  considered  as 
a  maximum  safe  working  depth,  and  at  that  depth  men  were 
not  permitted  to  work  more  than  an  hour  on  one  shift.  So  far 
as  the  writer  has  any  knowledge,  the  greatest  pressure  actually 
employed  in  compressed-air  work  was  52  pounds,  correspond- 
ing to  a  head  of  120  feet,  in  the  construction  of  the  East  River 
Gas  Company's  tunnel  under  the  East  River,  at  New  York. 
There  the  ordinary  pressure  was  about  45  pounds,  correspond- 


2l6  MODERN    TUNNEL    PRACTICE 

ing  to  a  head  of  104  feet.  At  the  Limfjord  bridge,  in  Den- 
mark, men  worked  for  some  time  at  a  depth  of  1 1 3  feet. 

During  the  earlier  stage  of  construction  of  the  Hudson  River 
tunnel,  in  1890,  a  compressed-air  hospital  lock  was  established 
at  the  New  Jersey  entrance  for  the  treatment  of  workmen  who 
were  suffering  from  the  effects  of  high  air  pressure.  At  this 
work  the  pressure,  at  that  time,  did  not  exceed  33  pounds  per 
square  inch,  but  some  of  the  men  suffered  severely  from  partial 
paralysis,  or  "the  bends,"  as  it  is  termed.  It  was  found  by 
experience  that  the  most  effectual  remedy  for  this  attack  was  to 
send  the  patient  back  into  the  working  chamber,  and  when  he 
had  recovered  from  the  attack,  to  bring  him  out  very  slowly 
through  the  air-lock. 

But,  as  the  air-lock  proper  is  constantly  required  for  other 
uses,  a  special  hospital  air-lock  was  constructed  for  this  pur- 
pose. This  was  simply  a  steel  cylindrical  shell  18  feet  long  and 
6  feet  in  diameter,  fitted  with  the  proper  doors,  inlet  and  outlet 
pipes,  etc.,  and  provided  with  beds.  The  cylinder  is  divided 
into  two  halves  by  a  center  diaphragm  with  a  door,  so  that  after 
the  patient  has  been  placed  under  the  effect  of  compressed  air  in 
the  inner  half  the  doctor  can  pass  out  through  the  other  half, 
operated  as  an  air-lock. 

Each  chamber  contains  two  narrow  beds,  and  beneath  the 
*floor  are  located  steam-radiating  pipes  for  heating  the  cham- 
bers. Incandescent  lamps  are  also  provided,  and  glass  win- 
dows permit  the  attendant  to  watch  the  patient  from  the  out- 
side. Fresh  air  is  provided  by  a  special  valve  arrangement,  and 
all  valves  are  controlled  from  the  outside  so  that  an  impatient 
workman  cannot  interfere  with  them  in  his  desire  to  get  out  at 
a  quicker  rate  than  is  safe.  In  releasing  the  patient  from  the 
lock,  two  or  more  hours  are  consumed  in  letting  off  the 
pressure. 

A  most  valuable  report  upon  the  effect  of  compressed  air 
upon  the  human  system  was  made  in  1871,  by  Andrew  H. 
Smith,  M.D.,  Surgeon  to  the  New  York  Bridge  Company,  then 
sinking  the  foundations  for  what  is  now  known  as  the  Brook- 
lyn Bridge,  in  New  York.  Dr.  Smith  made  a  special  study  of 


AIR-LOCKS 


217 


Caisson  Shaft- 


5 


V      6'     61 


2l8  MODERN   TUNNEL   PRACTICE 

the  so-called  "caisson  disease/'  and  the  effects  of  high  atmos- 
pheric pressure  upon  the  workmen.  He  defines  the  disease  and 
its  symptoms  and  causes,  describes  his  method  of  treatment  and 
illustrates  his  deductions  by  a  large  number  of  actual  cases. 
He  recommends  and  describes  a  hospital  air-lock  very  similar 
to  that  used  at  the  Hudson  River  tunnel.  A.  Jaminent,  M.  D., 
Physician  to  the  St.  Louis  Bridge,  has  also  published  a  valuable 
report  on  "The  Physical  Effects  of  Compressed  Air." 

O'Rourke  Air-lock — The  air-lock  here  illustrated  was  de- 
signed and  used  by  John  F.  O'Rourke,  M.  Am.  Soc.  C.E.,  in 
sinking  various  foundations  in  New  York  City. 

These  locks  were  used  with  cylindrical  wooden  caissons,  also 
designed  by  Mr.  O'Rourke  and  worthy  of  description  first. 
Each  cylinder  was  6  feet  y\  inches  outside  diameter  and  was 
made  up  of  staves  cut  with  radial  sides  and  having  inside 
angle-iron  hoops  bolted  to  the  staves.  The  staves  were  made 
of  4  x  6-inch  plank,  dressed  to  5!  x  3^  inches,  and  having  i- 
inch  square  slip  tongue  joints.  Any  two  lengths  of  this  cylin- 
der were  connected  by  a  double  angle  joint.  The  roof  of  the 
working  chamber  was  made  by  a  ring-shaped  diaphragm  of 
steel  plate.  Attached  to  the  wooden  staves  at  the  outer  edge  by 
a  special  angle-ring  bolted  to  each  stave,  and  to  its  inside  edge, 
was  bolted  the  bottom  of  the  caisson  working  shaft,  as  shown 
in  Fig.  105. 

The  steel  caisson-shaft,  3  feet  in  diameter,  connects  the  air- 
lock with  the  working  chamber  at  the  base  of  the  wooden 
cylinder.  This  riveted  cylinder  is  specially  designed  with  the 
object  of  providing  a  shaft  that  has  no  interior  projections  lia- 
ble to  catch  or  obstruct  the  hoisting  of  the  bucket.  But  as  it 
must  also  be  used  as  a  "man-shaft,"  Mr.  O'Rourke  devised  a 
ladder  which  fills  the  first-named  condition  of  non-obstruction. 
In  one  side  of  the  cylinder  is  cut  a  series  of  horizontal  oblong 
holes,  at  a  convenient  distance  apart  and  one  above  the  other, 
so  as  to  form  a  "ladder."  To  prevent  the  escape  of  air  at  these 
holes  a  continuous,  trough-like  cover  plate  is  riveted  outside  of 
these  holes,  and  far  enough  away  from  the  side  to  allow  the 
hand  or  foot  to  be  inserted  in  the  slots. 


AIR-LOCKS 


219 


The  air-lock  (Fig.  106)  is  cylindrical  in  form,  with  a  top 
and  bottom  opening  B  and  C.  Around  the  top  opening  is  a 
circular  inside  ring  D ;  this  opening  is  closed  by  the  oppositely 


I  f 

Elevation.  Sectional  Elevation. 

FIG.  106.— The  O'Rourke  Air-lock:  Details. 

arranged,  convex,  swinging  gates  E,  the  meeting  edges  being 
packed  so  as  to  form  an  air-tight  joint.     The  outer  edges  of 


22O  MODERN    TUNNEL    PRACTICE 

these  gates  are  provided  with  flanges  F,  which  close  against 
the  ring  D ;  the  flanges  having  flap-gaskets  projecting  into  the 
lock  so  that  the  air  pressure  forces  them  against  D.  Ordinarily, 
all  the  pressure  on  the  doors  E  is  taken  by  the  shaft  G;  yet  the 
ring  D  may  be  made  to  act  as  an  emergency  bearing  to  take  the 
pressure. 

The  gates  E  are  cut  away  at  the  center  of  the  meeting  edges, 
as  shown  at  H,  to  receive  and  fit  snugly  upon  the  stuffing-box 
J,  banded  with  rubber  and  having  a  hole  through  the  center 
for  the  hoisting  rope.  The  gates  E  are  hung  by  the  arms  K 
to  the  common  shaft  G;  one,  M,  being  fixed  to  the  shaft  and 
the  other,  N,  running  loose.  This  arrangement  by  means  of  the 
bevel-gear  and  idler,  m  n  o,  allows  the  two  doors  to  be  moved 
in  unison  and  in  opposite  directions.  This  hanging  of  the  gates 
on  a  single  center  obviates  the  necessity  of  piercing  the  shell 
in  more  than  two  places,  and  reduces  leakage.  The  drawings 
show  how  the  shaft  G  is  rotated  by  the  levers  0 ,  the  latter  be- 
ing counter- weighted  so  that  one  man  can  operate  the  lock. 

The  air-lock  has  its  lower  end  closed  by  similarly  oppositely 
arranged  swinging  gates  P,  with  seats  Q  fitting  against  the 
ring  R.  The  castings  forming  the  ring  Q  have  flanges,  q  r  s, 
which  continue  the  shaft-ladder  already  described,  and  are 
themselves  continued  by  the  ladder-like  structure  5. 

Unlike  the  upper  gates  E}  the  lower  gates  P  are  swung  by 
the  arm  T,  from  separate  shafts  U  and  V.  The  gate-arms  are 
rigidly  fixed  to  these  shafts  and  turn  with  them.  To  secure 
opposite  motion  to  the  shafts,  one  is  operated  by  a  spur-wheel 
from  the  other,  as  showrn  at  t  and  v,  operated  by  the  lever  0. 

The  admission  and  discharge  of  air  from  the  lock  is  con- 
trolled by  the  three-way  cock  X,  operated  by  a  lever  and  bevel- 
gear  and  connected  with  suitable  piping  to  the  air-shaft.  There 
are  no  independent  connections  with  the  compressors,  as  usual. 

To  operate  the  lock,  the  bucket  being  at  the  bottom  and  the 
bottom  gates  P  necessarily  open,  the  bucket  is  raised  up  into 
the  air-lock  and  the  bottom  gates  P  are  closed  behind  it.  The 
air  is  then  discharged  by  the  valve  X  from  the  lock  and  the  top 
gates  E  are  opened.  This  allows  the  bucket  to  be  hoisted  out 


AIR-LOCKS 


221 


and  dumped  or  loaded.     In  the  return  process  the  bucket  is 
hoisted  into  the  lock  and  the  top  gates  are  closed,  care  being 


Section  M-N. 

FIG.   107. — The  Zschokke  and  Terrier  Air-lock:   Mirabeau  Bridge,  Paris. 
Elevation  and  Plan. 

taken  to  fit  the  rope  in  the  stuffing-box  /.     The  air  pressure 
being  admitted,  the  bottom  gates  are  opened  and  the  bucket 


222 


MODERN    TUNNEL    PRACTICE 


descends  into  the  working  chamber.  This  whole  operation 
usually  takes  about  ten  seconds  and  is  accomplished  by  one 
man. 

When  the  bucket  is  at  the  bottom  everything  is  clear  open 


Elevation. 


FIG.  I07a. — The  Zschokke  and  Terrier  Air-lock :  sections. 

to  the  top  of  the  air-lock,  and  in  case  of  a  sudden  inrush  of 
water  the  men  can  escape  up  the  ladder  and  into  the  lock.  The 
lock  and  air-shaft  can  be  removed  and  used  again. 

Air-lock,  Mirabeau  Bridge,  Paris — The    river    piers  of  this 
bridge  were  founded  upon  metallic  caissons,  33  x  92  feet  in 


AIR-LOCKS  223 

their  dimensions,  sunk  by  compressed  air  to  a  hard  chalk  stra- 
tum 54  feet  below  the  water  line. 

The  working  chamber  is  about  6|  feet  high  and  is  connected 
with  the  open  air  by  four  shafts.  The  two  middle  shafts,  2.8 
feet  diameter,  are  fitted  with  air-locks  of  the  ordinary  type,  and 
are  used  by  the  workmen.  The  two  end  shafts  are  used  for 
removing  the  material ;  they  are  each  3.4  feet  in  diameter  and 
terminate  in  the  Zschokke-Terrier  air-locks,  shown  in  Figs. 
107  and  ro/a. 

These  latter  locks  are  designed  for  rapid  operation  and 
would  be  dangerous  if  used  by  the  workmen,  owing  to  the  quick 
changes  in  pressure.  The  bucket  A  rests  on  two  trunnions,  on 
racks  B  attached  to  the  frame  C ;  the  latter  carrying  at  its  lower 
end  a  plate  D,  which  closes  the  bottom  of  the  chamber  E.  This 
frame  is  suspended  by  a  chain,  one  end  of  which  is  fixed  to  the 
top  of  the  chamber  and  is  fitted  with  a  relieving  spring.  This 
chain  passes  down  under  a  pulley  fixed  to  the  bucket  frame; 
then  over  a  small  grooved  wheel  in  the  top  of  the  chamber,  and 
then  runs  down  the  shaft,  as  shown.  The  shaft  of  the  grooved 
wheel  last  referred  to  extends  outside  the  chamber,  and 
terminates  in  a  wheel  driven  by  a  friction  wheel  on  a  small  com- 
pressed-air engine  located  on  top  of  the  lock.  By  this  means 
the  chain  is  raised  or  lowered. 

When  the  filled  bucket  reaches  the  top  of  the  shaft,  the  latter 
is  closed  by  the  plate  D  fitting  against  a  rubber-faced  steel- 
ring.  A  valve  automatically  opens  which  allows  the  compressed 
air  to  escape  from  the  chamber;  and  as  soon  as  this  is  done 
a  swinging  door  is  opened  in  the  side  of  the  chamber  and  the 
bucket  is  dumped.  The  door  is  then  closed,  the  compressed  air 
is  let  into  the  chamber  again  and  the  bucket  descends  by  its  own 
weight. 

As  shown  on  the  plan,  the  chain  runs  down  a  special  conduit 
of  wrought  iron,  made  air-tight. 

Hughes  Air-lock — The  late  John  Hughes,  M.  Inst.  C.E.,  de- 
vised the  plan  here  described  for  sinking  wrought-iron  cylin- 
ders for  an  iron  pier  built  by  him  at  Valparaiso,  Chili,  in 
-83.  The  water  was  generally  48  feet  deep,  but  some 


224 


MODERN    TUNNEL    PRACTICE 


of   the    cylinders   were    sunk    107    feet   below    the    surface   of 
water. 

The  wrought-iron  cylinders  were  n  feet  4  inches  outside 
diameter,  made  in  sections  8  feet  long  and  connected  by  angle- 
iron.  Each  cylinder  had  an  inner  cylinder  8  feet  in  diameter. 


FIG.  108.— The  Hughes  Air-lock  and  Shaft :  Employed  at  Valparaiso,  Chili. 

The  cylinders  were  assembled  on  a  temporary  staging,  with 
the  inner  cylinder  bolted  to  the  top  of  the  working  chamber  and 
the  annular  space  made  water-tight.  With  the  cylinder  float- 
ing by  reason  of  the  annular  space,  a  wrought-iron  diaphragm 


AIR-LOCKS  225 

was  bolted  onto  the  top  of  the  inner  cylinder,  and  on  this  plate 
were  bolted  two  3-foot  cylinders.  When  the  bottom  had  been 
reached  the  annular  space  between  the  cylinders  was  filled  with 
Portland  cement  concrete,  and  all  the  cylinders  were  lengthened 
as  needed  to  keep  the  tops  above  the  water  level. 

The  air-locks  A  surmounted  the  two  smaller  shafts.  In  each 
the  top  door  was  opened  downward  by  an  outside  lever  at- 
tached to  the  prolongation  of  the  hinge-bar  and  passing  through 
a  stuffing-box.  A  ring  with  an  india-rubber  gasket  was  at- 
tached to  the  bottom  of  the  lock  and  the  top  of  the  skip-case  B 
made  an  air-tight  joint  with  the  lock  when  hoisted.  This  skip- 
case  was  suspended  by  two  chains  of  gaged  links,  one  on  each 
side,  and  these  chains  passed  over  the  chain-sheaves  C  to  the 
skip-case  at  the  bottom  of  the  adjoining  lock. 

The  lengths  of  chain  were  accurately  adjusted,  so  that 'when 
both  locks  are  closed  at  the  top  one  skip-case  can  be  made  to 
descend  and  the  other  ascend,  by  means  of  a  wrench  on  the  out- 
side, with  the  shaft  passing  through  stuffing-boxes.  When  the 
skip-case  B  strikes  the  bottom  of  the  lock,  the  compressed  air 
may  be  let  out  of  that  lock  and  the  skip  in  the  case  is  hoisted 
out  when  the  top  door  is  opened.  The  air  pressure  below 
forces  the  skip-case  B  tightly  against  the  ring  mentioned. 

The  skips  for  material  fit  closely  in  the  case  and  they  were 
hoisted  out  by  a  steam  crane.  A  pipe  was  run  through  each 
skip  near  the  bottom ;  as  the  skip  was  hoisted  out  of  the  lock  a 
bar  of  iron  was  pushed  through  this  pipe,  and  to  the  ends  of 
"this  bar  the  dumping  chains  were  attached.  Two  men  only 
worked  at  one  time  under  the  air  pressure,  and  these  in  4-hour 
shifts.  Though  a  depth  of  107  feet  below  the  water  surface 
was  reached  in  some  cylinders,  only  one  death  occurred.  This 
death  was  due  to  the  fact  that  the  man  failed  to  give  the  proper 
signal;  and  the  top-men,  supposing  only  material  was  to  be 
handled,  released  the  air-pressure  too  suddenly. 

Hyde  Park  Tunnel  Air-lock — The  air-lock  here  illustrated 
was  used  in  building  the  Hyde  Park  tunnel  for  the  Chicago 
Water  Works;  Samuel  G.  Artingstall,  M.  Am.  Soc.  C.E.,  Chief 
Engineer. 


226 


MODERN    TUNNEL    PRACTICE 


In  this  work  the  shafts  sunk  in  the  two  cribs  were  made  of 
cast-iron  cylinders,  10  feet  diameter  and  bolted  together  in  8- 


i"Cock 


Plan. 
FIG.  109.— Air-lock  Used  at  Top  of  Shaft:  Hyde  Park  Tunnel,  Chicago. 

foot  sections.     After  the  shafts  had  been  sunk  to  the  tunnel 
level  and  the  tunnel  had  been  driven  about  800  feet  from  the 


AIR-LOCKS 


227 


228  MODERN    TUNNEL    PRACTICE 

shaft,  water  broke  into  both  drifts.  An  air-lock  was  then 
placed  in  the  drifts  and  the  work  continued  under  air  pressure. 
This  air-lock  is  shown  in  plan  and  elevation  in  Fig.  no,  and 
needs  little  description. 

To  re-enter  the  portion  of  the  flooded  tunnel  lying-  west- 
ward from  the  outer  crib,  an  air-lock  was  placed  on  top  of  the 
shaft.  This  lock,  Fig.  109,  is  also  here  shown  in  sufficient 
detail  to  explain  its  construction. 

Morison  Air-lock — The  lock  here  described  was  used  by 
George  S.  Morison,  M.  Am.  Soc.  C.E.,  in  sinking  the  pier  foun- 
dations for  the  Memphis  Bridge  over  the  Mississippi  River. 
The  masonry  piers  were  sunk  on  wooden  caissons,  39  to  59  feet 
high,  and  reaching  to  93  feet  below  low-water  mark,  including 
the  masonry  piers. 

Each  caisson  was  provided  with  four  24-inch  shafts  for  re- 
moving material  and  finally  for  sending  in  concrete  to  fill  the 
working  chamber.  Besides  these  shafts  there  was  a  36-inch 
shaft  with  a  double  air-lock  at  the  bottom,  of  the  ordinary  type; 
and  a  6-foot  shaft  with  a  special  air-lock  at  the  bottom,  fitted 
with  an  elevator  cage  for  the  use  of  the  men. 

The  clay  was  removed  by  the  "clay  hoist,"  Fig.  in.  This 
air-lock  was  placed  at  the  top  of  the  shaft,  and  behind  it  was  a 
cylinder  and  piston ;  the  speed  of  the  piston  being  multiplied  by 
two  sets  of  sheaves  so  that  the  stroke  of  the  piston  would  lift 
a  bucket  from  the  bottom  of  the  caisson  to  the  "air-lock  on  top. 
This  air-lock  is  provided  with  two  doors ;  the  one  opening  into 
the  shaft  below  is  closed  by  a  lever  with  a  balance  weight  on 
the  outside.  The  other  door,  opening  into  the  open  air,  is 
worked  by  a  man  stationed  outside. 

The  only  power  used  was  the  air  pressure  in  the  caisson,  ad- 
mitted to  the  bottom  of  the  piston  case  by  appropriate  pipes  and 
valves.  The  bucket  carried  6J  cubic- feet,  and  12  buckets  per 
hour  were  passed  out  at  a  single  hoisting  shaft.  Four  hoists 
were  provided,  but  only  two  were  used  at  one  time. 

The  special  air-lock,  also  shown  in  Fig.  in,  was  fitted  with 
a  passenger  hoist,  which  was  operated  by  a  hoisting  engine 
placed  at  the  top  of  the  shaft;  and  this  engine  could  be  taken 


AIR-LOCKS 


229 


up  by  a  derrick  and  quickly  replaced  when  it  was  necessary  to 
add  a  section  to  the  shaft.  This  engine  was  also  driven  by  com- 
pressed air.  The  upper  shaft,  through  which  the  elevator  cage 
ran,  was  a  cylinder,  6  feet  in  diameter.  The  air-lock  was  also 
6  feet  in  diameter,  and  the  shaft  leading  to  the  caisson  was  4 


FIG.    in. — Memphis   Bridge:    Details   of   Air-lock   and   Hoists. 

feet  in  diameter.  These  three  cylinders  were  set  side  by  side, 
with  the  shells  connected  by  doors ;  while  a  fourth  door  opened 
outward  at  the  bottom  of  the  lower  shaft.  In  working,  the 
door  between  the  two  upper  shafts  was  always  kept  closed,  and 
the  door  in  the  bottom  shaft  was  open.  In  an  emergency  the 
lower  shaft  could  be  used  as  an  air-lock  by  itself. 


230  MODERN    TUNNEL    PRACTICE 

Victoria  Bridge  Air-lock — The  Victoria  Bridge  was  built  in 
1892  by  Charles  Neate,  M.  Inst.  C.E.,  at  Stockton-on-Tees, 
England.  The  piers  were  founded  on  five  cast-iron  cylinders 
for  each  pier,  each  cylinder  14  feet  in  diameter.  The  larger 
part  of  the  sinking  was  done  by  the  pneumatic  process. 

The  main  cylinder  of  the  air-lock  (Fig.  112)  was  8  feet  high 
and  5  feet  diameter,  fitted  with  a  partly  boarded  floor,  but 


FIG.  112.— Victoria  Bridge:  Air-lock. 


otherwise  open  to  the  working  chamber.  The  air-lock  proper 
was  formed  by  a  lateral  chamber  with  two  doors,  as  usual.  On 
the  side  opposite  to  this  is  a  vertical  cylinder,  5^  feet  in  height 
and  1 8  inches  diameter.  This  cylinder  is  open  at  the  top  and 
carries  a  piston  operated  by  compressed  air,  and  the  piston-rod 
carries  a  rack  which  actuates  a  pinion  and  thus  revolves  a 
sheave  keyed  to  the  shaft  inside  the  main  cylinder.  The  ex- 


AIR-LOCKS 


23I 


cavated  material  is  raised  by  a  rope  passing  over  this  sheave, 
the  rope  rising  10  feet  for  every  i-foot  lift  of  the  rack. 

This  raised  material  was  to  be  dumped  into  a  discharge  spout 
fixed  in  the  side  of  the  main  cylinder  and  fitted  with  the  proper 
doors.  But  while  a  similar  spout  was  used  for  passing  in  the 
concrete,  it  was  found  advisable  to  pass  the  excavated  material 
through  the  air-lock  proper.  With  this  exception,  this  pneu- 
matic machinery  worked  well.  The  concreting  was  carried  up 
within  12  feet  of  the  lock-floor  before  the  lock  was  removed. 
The  material  excavated  was  a  fine  running  sand. 

Air-locks  at  Kiel  Dry-dock — The  German  Government  has 
lately  completed  at  Kiel,  a  concrete  dry-dock  in  which  the  sub- 
aqueous work  was  performed  by  means  of  a  floating  pneumatic 
caisson. 

In  connection  with  this  device  two  forms  of  air-locks  were 
used,  one  for  passing  in  concrete  and  material,  the  other  for  the 
use  of  the  workmen.  The  latter  lock  is  shown  in  Fig.  113,  and 


Longitudinal    Section. 

Cross  Section. 
FIG.    113.— Kiel   Dry-dock:  Air-lock  for  Workmen. 

it  constitutes  a  double  air-lock;  the  outer  chamber  containing 
four  men,  while  both  chambers  together  will  accommodate 
twelve  men. 

The  special  and  altogether  novel  feature  in  this  lock  is  an 
arrangement  of  valves  designed  to  permit  the  gradual  auto- 


232 


MODERN   TUNNEL   PRACTICE 


matic  equalization  of  pressure  between  the  inside  and  outside 
of  the  lock.  The  valves  are,  in  fact,  automatic  regulators  and 
they  are  operated  as  follows:  When  entering  the  lock,  the 
device  gives  a  uniform  pressure  increase  of  1.5  pounds  per 
minute;  when  locking-out,  the  uniform  decrease  in  pressure  is 
only  f  of  a  pound  per  minute.  This  attachment  to  the  air-lock 
prevents  the  possibility  of  injury  to  workmen  as  a  result  of  the 
too  rapid  transition  to  or  from  the  compressed-air  chamber. 

As  here  shown  in  Fig.  1 14,  the  valve  has  a  small  air  passage 
B  regulated  by  the  needle  E.  This  needle  is  attached  to  a  small 
piston  C  acted  on  by  the  higher  pressure  on  one  side,  and  the 
lower  pressure  on  the  other.  The  latter  pressure  is  aided  by  a 
coil-spring,  which  tends  to  force  the  piston  to  the  end  opposite 
the  air-passage  B,  and  thus  opens  the  needle  passage.  The 
actual  position  of  the  needle  at  any  time  thus  depends  upon  the 
difference  of  air-pressure  on  the  two  sides. 

Two  valves  are  connected  with  each  air-lock,  one  for  locking- 


FIG.  114. — Air-valve  for  Slow  Pressure    Equalization  in  Kiel  Air-locks. 

in  and  the  other  for  locking-out.  In  the  first  case,  the  com- 
pressed air  from  the  supply  main  enters  at  A,  passes  through  B 
to  the  discharge  openings  at  E  leading  into  the  air-lock.  The 
air  from  A  also  passes  around  behind  the  valve-piston  and 
presses  the  needle  forward  to  a  point  where  it  is  balanced  by 
the  pull  of  the  coil-spring  added  to  the  air  pressure  in  the  lock. 
As  the  lock-pressure  increases  gradually,  the  piston  is  forced 
back  and  the  opening  at  B  is  enlarged. 

The  valve  for  locking-out  is  connected  to  the  air-lock  by  the 
opening  A,  and  with  the  external  air  by  the  opening  E.  The 
operation  is  similar  to  that  described  above.  A  separate. 


AIR-LOCKS 


233 


smaller  valve,  however,  admits  fresh  compressed  air  to  the  lock 
at  half  the  rate  of  the  escaping  air,  so  that  the  effective  pressure 


•g Longitudinal  Section.  £Side  Elevation, 

FIG.  115. — Kiel  Drydock:  Counterbalanced  Material  Elevators. 


234  MODERN    TUNNEL    PRACTICE 

decrease  is  only  f  of  a  pound  per  minute,  or  half  the  pressure 
increase  in  locking-in. 

With  a  caisson-pressure  of  30  pounds  per  square  inch,  the 
operation  of  locking-in,  with  this  regulator,  required  20  min- 
utes. The  locking-out  consumed  40  minutes.  These  rates 
would  be  deemed  excessively  slow  in  American  caisson  practice, 
but  the  use  of  the  same  principle  could  be  utilized  with  a 
valve  permitting  a  more  rapid  equalization. 

These  regulator  valves  are  made  by  Korting  Brothers,  Han- 
over, Germany.  The  engineer  in  charge  at  Kiel  said  that  "in 
general  they  gave  very  good  satisfaction."  But  he  said  that 
they  sometimes  failed  in  cold  weather,  by  reason  of  ice  forming 
at  the  needle  aperture.  Ordinary  air-cocks  were  found  useful 
in  giving  the  sudden  increase  pressure  necessary  to  tightly  close 
the  door ;  after  that  the  time- valve  was  used.  These  ordinary 
cocks  could  only  be  manipulated  with  special  keys  in  the  posses- 
sion of  the  inspectors  and  lock-tenders. 

Seven  vertical  shafts  of  riveted  steel  pipe  connected  the 
working  platform  of  the  floating  pneumatic  caissons  with  the 
suspended  working-chamber  below.  These  shafts  were  made 
in  sections,  so  that  they  could  be  added  or  removed  as  the  work- 
ing-chamber was  lowered  or  raised;  weight  being  added  or 
removed  by  pumping  water  into  or  out  of  cylindrical  balance- 
tanks,  in  the  upper  half  of  the  working-chamber.  Four  of  these 
seven  shafts  were  used  for  handling  material,  two  were  for 
workmen,  and  one  was  for  concrete.  All  of  these  shafts  had 
air-locks  at  the  upper  end  and  they  were  closed  by  air-tight 
doors  at  the  bottom  when  changes  were  being  made  in  length. 
Of  the  four  material  shafts,  two  were  fitted  with  motor-driven 
elevators,  while  two  merely  had  doors  at  the  top  and  bottom, 
allowing  them  to  be  utilized  as  a  full-length  air-lock  in  passing 
long  timbers  into  the  working-chamber. 

The  concrete  shaft  forms  a  simple  chute,  with  a  lining  tube, 
down  which  the  concrete  falls.  This  chute  is  kept  full  of  con- 
crete, and  two  lateral  hoppers  at  the  bottom  permit  the  contents 
to  be  tapped  as  needed  into  buckets  running  on  overhead  trol- 
leys in  the  working-chamber.  The  upper  end  of  the  chute  is 


AIR-LOCKS  235 

fitted  with  a  double  hopper,  both  compartments  of  which  dis- 
charge into  the  inner  lining  of  the  tube.  These  two  compart- 
ments are  filled  alternately  and  each  has  an.  air-tight  trap  door 
at  top  and  bottom,  so  that  one  can  be  filled  while  the  other  is 
discharging  into  the  chute.  These  two  sets  of  doors  are  inter- 
locked so  that  only  one  can  be  opened  at  a  time.  The  small  air- 
lock at  the  side  of  the  top  end  of  the  chute  serves  to  admit  two 
laborers  into  the  space  just  beside  the  hopper,  for  operating  the 
bottom  doors  of  the  hopper  compartments. 

The  two  material  elevators  are  arranged  as  shown  in  Fig. 
115.  The  two  shafts,  side  by  side,  are  fitted  with  two  hoisting 
skips,  counterbalanced  through  their  connection  to  the  same 
hoisting-motor  shaft.  By  a  worm-gearing  this  shaft  drives  a 
lifting  sheave  over  the  center  of  each  shaft,  a  sprocket  chain  at- 
tached to  the  skip  passing  over  this  sheave.  The  slack  in  the 
chain  is  taken  up  by  a  three-post  rigging  held  taut  by  a 
weight  contained  in  a  small  air-tight  auxiliary  well  at  the  side 
of  the  main  shaft.  The  hoisting  motor  is  automatically  shut  oft" 
and  a  brake  is  applied  when  either  skip  nears  its  highest  posi- 
tion. To  draw  the  skip  up  so  that  its  bottom  plate  forms  an  air- 
tight seal  against  the  bottom  ring  of  the  air-lock,  a  hand-hoist 
is  thrown  into  gear  by  a  foot-lever,  which  latter  also  releases 
the  brake. 

The  skip  is  a  skeleton  frame  carrying  a  horizontal  track  rail, 
on  which  runs  a  trolley  carrying  the  bucket.  When  the  skip 
is  at  the  top  or  bottom  this  rail  registers  with  a  similar  track- 
rail,  and  the  bucket  is  thus  quickly  run  into  or  out  of  the  skip- 
frame. 


'  CHAPTER  XIII 

TUNNEL  NOTES 

The  freezing  process  for  shaft-sinking — Its  application  at  Ronnenberg  and 
at  Iron  Mountain — Tunnel  rock-temperatures — Definition  of  quick- 
sand— Making  concrete  water-tight — The  hand-auger  in  prospecting 
work — Tunnel  cross-section  instrument — Coxe's  plummet-lamp. 

The  Freezing  Process  for  Shaft-sinking — This  process  was  in- 
vented by  F.  A.  Poetsch,  a  German  engineer,  and  was  first  suc- 
cessfully employed  by  him  in  1883-4,  at  the  Archibald  lignite 
mine,  at  Schneicllingen,  Germany.  The  process  is  expensive 
and  is  only  used  in  penetrating  water-bearing  strata  where 
other  and  less  costly  methods  fail. 

This  method  of  shaft-sinking  may  be  generally  described  as 
follows :  Around  the  site  of  the  proposed  shaft  and  at  some 
little  distance  outside  of  the  dimensions  determined  upon,  is 
sunk  a  circle  of  pipes,  6  to  8  inches  diameter,  and  penetrating 
the  rock  or  other  impermeable  material  underlying  the  water- 
bearing stratum.  The  sinking  of  these  pipes  is  one  of  the  ex- 
pensive features  of  the  plan,  as  boulders  and  other  obstructions 
may  be  encountered.  When  sunk  these  larger  pipes  are  closed 
tightly  at  the  bottom,  and  in  the  center  of  each  is  inserted  a 
smaller  circulating  pipe,  not  quite  so  long  as  the  large  pipe  and 
open  at  the  bottom.  At  the  top,  these  two  systems  of  pipes 
are  then  connected  by  other  pipes  leading  to  the  brine  pump. 
With  the  pipe  system  in  place  a  freezing  solution  is  forced  by 
the  pump  down  the  inner  tube  and  up  in  the  annular  space  sur- 
rounding this  inner  tube.  The  final  result  of  circulating  this 
saline  solution  through  the  pipes  is  to  extract  whatever  heat 
there  is  in  the  soil  surrounding  the  pipes,  and  after  a  sufficient 
time  to  freeze  solidly  a  ring  of  material  surrounding  the  site  of 

236 


TUNNEL    NOTES 

the  shaft,  this  ring  excluding  the  outside  water  and  permitting 
excavation  and  lining  in  the  open. 

The  freezing  operation  is  kept  up  until  the  work  has  ad- 
vanced sufficiently  to  avoid  all  danger  from  thawing.  As  the 
shaft  built  will  in  time  again  be  surrounded  by  water-bear- 
ing material,  the  lining  must  be  made  water-tight  by  iron  cylin- 
ders or  other  construction;  and  the  connection  with  the  rock 
at  the  bottom  must  also  be  made  so  as  to  permanently  exclude 
water.  With  this  general  description,  the  method  is  further 
explained  in  the  specific  cases  here  noted. 

Freezing  Process  at  Ronnenberg1. — Soundings  made  by  the 
Alkali  Society  of  Ronnenberg,  Germany,  showed  that  a  bed  of 
salts  of  potash  lay  at  a  depth  of  459  feet  below  the  surface. 
To  the  depth  of  407  feet  the  ground  was  largely  composed  of  a 
much  fissured  and  very  irregular  gypsum  formation  permeated 
with  water;  a  50- foot  bed  of  hard  and  compact  gypsum  lay 
immediately  over  the  salt  formation. 

After  the  failure  of  other  methods  it  was  determined  to  try 
the  freezing  process.  But  as  the  water  met  with  contained  3% 
of  salt  at  a  depth  of  105  feet,  some  experiments  were  made  to 
ascertain  whether  the  freezing  process  would  be  successful 
under  these  conditions.  Tests  were  made  with  saline  solutions 
of  4,  8,  10  and  12%  of  NaCl;  and  these  solutions  were  sub- 
mitted for  24  hours  to  a  temperature  of  I2°C.  At  the  end  of 
this  time  it  was  found  that  the  4%  solution  was  almost  solidly 
frozen;  the  others  less  so,  and  the  12%  solution  was  little 
affected  by  the  cold  at  the  end  of  48  hours. 

The  installation  included  30  tubes  sunk  to  a  depth  of  413 
feet  in  a  circle  29^  feet  in  diameter.  The  freezing  machines 
were  double  the  capacity  of  a  plant  intended  for  a  non-saline 
soil.  Five  months  were  consumed  in  sinking  the  tubes  and  in 
making  the  necessary  connections;  and  in  39  days  after  the 
actual  freezing  operation  was  commenced,  the  temperature  at 
the  bottom  of  the  shaft  was  4°C.  The  machines  were  kept  in 
operation  for  20  days  longer  before  the  excavating  of  the  shaft 
was  started,  and  after  considerable  work  had  been  done  upon 
the  shaft  one  of  the  two  freezing  machines  was  stopped.  The 


238  MODERN    TUNNEL    PRACTICE 

excavation  near  the  wall  of  the  shaft  was  done  by  hand,  explo- 
sives being  used  carefully  in  the  central  core.  The  inside  diam- 
eter of  the  masonry  lining  of  the  shaft  was  18  feet. 

Mining  Shaft  at  Iron  Mountain,  Mich. — Mr.  Charles  Sooy- 
smith,  M.  Am.  Soc.  C.E.,  as  the  owner  of  the  Poetsch  patents 
in  the  United  States,  has  made  a  very  careful  study  of  this 
method,  and  the  following  notes  relate  to  his  experience  in  sink- 
ing a  mining  shaft  at  Iron  Mountain,  Mich. : 

At  this  shaft  8-inch  pipes  were  sunk  in  a  circle  29  feet  in 
diameter,  through  water-bearing  soil,  to  a  depth  of  about  90 
feet.  The  material  was  coarse  and  fine  sand,  with  occasional 
layers  of  boulders. 

Chloride  of  calcium  brine,  cooled  by  an  ice-machine  to  about 
5°F.,  was  circulated  through  the  system  of  pipes  installed.  In 
39  days  the  frozen  area  extended  4  feet  5  inches  outside  the 
circle  of  pipes  and  to  a  somewhat  greater  distance  inside.  In 
70  days  the  inside  distance  was  1 1  feet  from  the  circle  of  pipes. 
As  the  frozen  wall  was  unnecessarily  thick  the  ice-machine  was 
only  run  sufficiently  to  maintain  the  wall  secured.  This  wall 
did  not  thaw  out  sufficiently  to  admit  any  water  until  50  days 
after  the  completion  of  the  shaft. 

From  experiments  made  Mr.  Sooysmith  concludes  as  fol- 
lows :  But  a  small  proportion  of  the  cold  will  be  expended  in 
cooling  the  earth  outside  of  the  frozen  mass.  For  example,  if 
the  material  is  frozen  5  feet  outside  the  line  of  excavation  neces- 
sary, it  would  require  only  about  12%  of  the  total  freezing 
capacity  to  cool  the  material  for  a  distance  of  8  feet  outside  of 
the  frozen  mass  from  a  temperature  of  32°F.  to  i°F.  below  the 
normal  temperature  of  the  material.  The  interior  of  the  frozen 
mass  is  cooled  far  below  the  freezing  point,  and  so  acts  as  a 
reservoir  of  cold.  It  should  be  remembered,  in  connection  with 
this  freezing  process,  that  a  cubic  foot  of  chloride  of  calcium 
brine  will — for  each  degree  of  temperature — carry  about  60 
thermal  units,  or  about  300  times  as  much  as  a  cubic  foot  of 
air  at  atmospheric  pressure.  As  the  circulating  pipes  are  in 
direct  contact  with  the  soil,  the  freezing  effect  is  correspond- 
ingly rapid.  The  absolute  conductivity  of  frozen  soil  is  about 


TUNNEL    NOTES  239 

20;  or,  20  British  thermal  units  will  pass  through  a  body  of 
frozen  soil  I  foot  square  and  I  inch  thick  in  one  hour  with  a 
difference  of  temperature  of  i°F. 

Tunnel  Temperature. — In  the  Simplon  tunnel  temperature 
observations  have  been  regularly  made,  taking  the  temperature 
of  both  the  rock  and  the  air  in  the  tunnel.  As  the  figures  as 
given  for  the  temperature  of  the  air  vary  largely  with  the 
amount  and  kind  of  ventilation,  the  following  average  temper- 
atures are  for  the  rock  only : 

North  Heading —  South  Heading— 

Dist.  from  portal,  Temp.  Dist.  from  portal,  Temp. 

feet.  Fahr.  feet.  Fahr. 

1,640  54.3°  1,640  56.2° 

3,280  57.5°  3,280  61.2° 

6,560  63.6°  6,560  69.7° 

9,840  70.3°  .     9,860  74.7° 

12,920  76.3°  11,150  86.9° 

15,090  86.3°  11,810  87.6° 

16,400  89.1° 

The  maximum  observed  temperatures  have  been  92.2°F.  in 
the  north  end,  and  88.7°F.  in  the  south  end.  The  water  flow- 
ing from  the  rock  has  sometimes  had  a  temperature  of  9i°F. 
The  normal  amount  of  ventilation  required  during  the  summer 
of  1901  was  about  39,000  cubic  feet  of  free  air  per  minute, 
forced  in,  at  the  north  end,  and  66,000  cubic  feet  per  minute 
at  the  south  end. 

What  Is  Quicksand  ? — One  of  the  most  troublesome  materials 
dealt  with  in  tunneling  operations  is  quicksand;  yet  there  are 
few  materials  about  which  there  is  such  a  diversity  of  opinion 
as  to  its  constituent  ingredients.  One  dictionary  defines  quick- 
sand as  "A  large  mass  of  loose  or  moving  sand  mixed  with 
water" ;  and  another  similar  authority  calls  it  "A  mixture  with 
water  of  rounded  particles  of  sand  and  clay,  the  sand  predomi- 
nating." 

Probably  the  best  discussion  of  the  real  character  of  quick- 


24O  MODERN    TUNNEL    PRACTICE 

sand  is  found  in  The  Transactions  of  the  American  Society  of 
Civil  Engineers,  Vol.  XLIII,  p.  582.  In  the  course  of  this 
discussion  Mr.  Allen  Hazen,  M.  Am.  Soc.  C.E.,  defines  quick- 
sand as  "An  even-grained  sand,  containing  for  the  time  far 
more  water  than  would  normally  be  contained  in  its  voids,  and, 
therefore,  with  its  grains  held  a  little,  distance  apart,  so  that 
they  flow  upon  each  other  readily."  Mr.  Hazen  goes  on  to  say 
that  this  sand  may  be  either  fine  or  coarse,  but  it  is  usually 
extremely  fine.  It  may  contain  a  little  clay  and  still  act  as 
quicksand ;  but  a  material  containing  considerable  clay  is  cohe- 
sive and  impervious  to  water.  Water  may  press  this  mixture  of 
clay  and  sand  out  of  place  or  make  cracks  in  it,  and  under  heavy 
pressure  it  may  flow  slowly.  But  such  a  compound  will  never 
make  an  intimate  liquid  mixture  with  water  capable  of  flowing 
through  small  openings  and  behaving  like  water.  This  latter  is 
the  characteristic  property  of  quicksand. 

Quicksands  are  usually  fine  sands,  says  Mr.  Hazen.  With  an 
effective  size  of  grain  from  0.20  to  0.30111111.,  an  upward  veloc- 
ity of  5  to  12  feet  per  second,  the  usual  velocity  of  ground 
water  about  an  excavation,  will  not  lift  the  sand.  It  would  re- 
quire an  unusually  strong  ground-water  current  to  make  sand 
of  this  coarseness  act  as  quicksand.  But  if  the  sand  grain  has 
a  diameter  of  o.iomm.,  it  only  requires  a  current  velocity  of 
1 6  inches  per  hour  to  lift  it,  and  this  velocity  is  very  common. 
When  sand  of  0.05  and  o.O3mm.  is  found  in  pervious  mater- 
ials, it  is  thus  sure  to  act  as  quicksand. 

Making  Concrete  Water-tight — The  increasing  use  of  con- 
crete for  tanks,  reservoirs  and  conduits  of  various  kinds  has 
naturally  turned  the  attention  of  engineers  to  securing  water- 
tight construction.  To  do  this  two  paths  are  open  to  the  engi- 
neer :  he  may  employ  some  form  of  waterproofing,  or  he  may 
so  manufacture  his  concrete  that  it  will  be  waterproof.  In 
actual  practice,  however,  the  latter  method  of  solving  the  prob- 
lem is  usually  a  very  expensive  and  difficult  operation.  We 
may  review  some  of  the  more  usual  processes  for  waterproofing 
concrete,  as  follows : 

The  most  common  practice  is  to  use  some  kind  of  asphalt 


TUNNEL    NOTES  24! 

coating,  employed  either  alone  or  in  combination  with  tarred 
or  asbestos  felt.  In  the  latter  case  the  felt  is  laid  to  break  joints 
and  the  asphalt  is  spread  under,  between  and  over  the  felt,  and 
the  whole  is  then  covered  by  concrete.  There  are  usually  three 
to  six  layers  of  felt,  and  the  asphalt  is  always  of  the  best  grade 
of  Bermuda  or  Alcatraz  lake-asphalt.  The  ultimate  durability 
of  this  waterproofing  is  yet  unknown,  though  it  is  extensively 
used  in  subway  work. 

When  asphalt  alone  is  used  the  concrete  surface  is  first  plas- 
tered with  a  rich  mortar,  on  which  the  asphalt  is  mopped  to 
a  thickness  of  £  inch,  and  then  plastered  over  before  the  re- 
mainder of  the  concrete  is  deposited.  Asphalt  mastic  is  usu- 
ally laid  directly  on  the  concrete  to  a  depth  of  about  \  inch, 
and  is  then  covered  directly  by  the  concrete. 

In  Europe,  where  many  tanks  and  conduits  have  been  built 
of  reinforced  concrete,  the  only  waterproofing  used  is  a  layer  of 
rich  cement  mortar  about  i  inch  thick.  This  mortar  coating 
is  preferably  built  up  with  the  concrete,  and  is  placed  on  the 
inside.  For  water  pressures  of  over  5o-foot  head,  European 
engineers  deem  it  necessary  to  line  with  sheet-steel  all  rein- 
forced cement  pipe ;  though  the  pipes  referred  to  usually  have 
very  thin  shells.  European  and  American  experience  with 
tanks  and  conduits  indicates  that  all  practical  requirements  for 
water-tightness  are  secured  by  a  wet  mixture  and  a  cement 
mortar  coating. 

A  number  of  experiments  have  been  made  in  producing  im- 
permeable concrete,  both  in  Europe  and  in  the  United  States. 
The  object  was  either  to  determine  a  mixture  of  cement  and 
aggregates  that  would  resist  the  percolation  of  water,  or  to  dis- 
cover some  substance  that,  mixed  with  the  cement,  would  render 
the  hardened  product  impermeable.  Mr.  R.  Ferat,  of  the  Bou- 
logne Laboratory  of  the  Fonts  et  Chaussees,  after  five  years  of 
experimenting,  came  to<  the  following  conclusions : 

"The  minimum  permeability  is  found  in  mortars  where  the 
proportion  of  medium-sized  grains  is  small,  and  the  coarse  and 
fine  grains  are  about  equal  to  each  other." 

His  experiments  also  showed  that  the  permeability  of  mor- 


242  MODERN    TUNNEL    PRACTICE 

tars  submitted  to  a  continuous  filtration  of  fresh  or  sea  water 
diminishes  rapidly  with  time.  He  also  advocates  a  too  large 
dose  of  mixing  water  rather  than  a  too  small  quantity.  Other 
experiments  tend  to  show  that  fine  sand  is  better  than  coarse 
sand,  and  with  the  same  sand  permeability  increases  as  the  pro- 
portion of  cement  increases. 

In  connection  with  the  admixture  of  other  materials  with  the 
cement,  Mr.  R.  W.  Lesley,  Assoc.  M.  Am.  Soc.  G.  E.,  advocates 
a  reasonable  proportion  of  slaked  lime  to  the  concrete  wrhen 
mixing.  The  experiments  of  Prof,  de  Smedt  show  that  this 
lime  does  not  injure  cements  or  mortars;  does  not  cause  ex- 
pansion; and  does  not  decrease  the  strength,  though  it  does 
slightly  retard  the  setting  of  the  mortar.  The  advantage  of 
the  lime  in  the  mass  is  that  it  tends  to  close  the  pores,  to  form 
efflorescence  or  deposits  on  the  surface,  and  should  largely  aid 
in  making  mortars  impermeable.  But  no  extended  experiments 
have  yet  been  made  exactly  in  this  line. 

Silicate  of  soda  and  soap  and  alum  have  been  mixed  with 
cement  in  an  attempt  to  make  the  mortar  water-tight.  Prof. 
W.  K.  Hatt  conducted  experiments  with  these  mixtures.  He 
found  that  the  effect  of  the  silicate  of  soda  diminished  the 
strength  of  the  mortar  more  than  50%,  and  diminished  the 
absorption  of  ash  mortars  about  50%.  The  soap  solution  alone 
does  not  increase  the  strength,  but  does  decrease  the  perme- 
ability about  50%.  The  effect  of  alum  and  soap  was  to 
strengthen  the  mortar  and  harden  it,  with  50%  decrease  in 
absorption.  Prof.  Hatt  used  a  5%  solution  of  ground  alum  and 
water,  and  a  7%  solution  of  soap  and  water.  The  alum  water 
was  mixed  with  the  mortar  in  the  proportion  of  one-half  the 
ordinary  gaging  water;  the  soap  solution  was  then  applied  to 
bring  the  mortar  to  the  desired  plasticity.  The  soap  and  alum 
acting  together  cause  the  precipitation  of  an  insoluble  com- 
pound in  the  pores  of  the  mortar. 

The  report  of  the  Chief  of  Engineers,  U.  S.  Army,  for  1902, 
contains  some  interesting  notes  on  the  waterproofing  of  con- 
crete, now  so  extensively  used  in  fortification  work.  Experi- 
ments made  at  Fort  Armistead,  near  Baltimore,  showed  con- 


TUNNEL    NOTES  243 

clusively  that  there  was  less  resistance  to  the  passage  of  water 
through  30  feet  of  concrete  than  to  its  passage  through  sandy 
soil. 

In  building  heavy  gun  emplacements  with  Portland  cement 
concrete,  the  use  of  asphalt  has  been  largely  abandoned  as  a 
waterproof  covering.  Instead,  a  coating  of  roofing  paint  is 
applied  over  the  concrete  steel  ceiling,  and  on  this  is  laid,  like 
shingles,  three  layers  of  asbestos  felt ;  this  is  again  coated  with 
roofing  paint,  and  then  covered  by  a  I  ^-inch  layer  of  poor  mor- 
tar, made  of  one  part  cement  to  six  parts  sand.  Above  this 
mortar  is  placed  ordinary  concrete.  It  is  expected  that  cracks 
will  not  extend  below  the  felt.  In  building  powder  magazines 
lead  sheets  are  used  instead  of  the  asbestos  felt. 

In  a  case  where  unequal  settlement  produced  cracks  in  the 
concrete,  linseed  oil  was  successfully  applied  on  the  surface. 
Large  cracks  were  filled  with  cement  grout,  and  the  linseed 
oil  was  applied  as  long  as  it  would  be  absorbed,  in  cracks  and 
on  the  surface. 

In  another  case,  asphalt  diluted  with  petroleum  residuum 
oil  was  used ;  and  the  groove  made  at  the  surface  of  the  con- 
crete, over  the  crack,  was  filled  with  asphalt. 

An  alum-and-lye  waterproof  wash,  employed  on  the  fortifi- 
cations at  the  mouth  of  the  Columbia  River,  was  made  as  fol- 
lows :  One  pound  concentrated  lye  and  5  pounds  of  alum  to 
2  gallons  of  water  constituted  the  "stock."  To  i  pint  of  the 
stock  10  pounds  of  cement  were  added,  thinned  out  with  water 
until  the  mixture  could  be  applied  with  a  kalsomine  brush. 
This  is  applied  to  the  plaster  until  it  fills  all  the  pores.  This 
surface,  if  too  dry,  should  be  wet  with  a  brush,  ahead  of  the 
waterproofing.  The  wash  should  be  applied  as  soon  as  pos- 
sible after  the  plaster  has  set,  but  never  when  the  walls  are 
too  warm  or  the  sun  is  shining  brightly.  It  will  not  adhere 
well  to  old  work.  .Two  coats  are  sufficient ;  and  plastered  con- 
crete so  coated  has  successfully  withstood  a  head  of  10  to  12 
feet  of  water  for  days  at  a  time. 

In  the  Pennsylvania  R.  R.  tunnels,  now  being  constructed  in 
New  York  City,  the  problem  of  waterproofing  these  tunnels 


244  MODERN    TUNNEL    PRACTICE 

has  been  deemed  of  sufficient  importance  to  warrant  the  issue 
of  special  and  revised  specifications  for  this  work.  An  abstract 
of  the  specifications  follows  : 

The  tunnel  lining  will  be  concrete  walls,  filled  in  behind  suit- 
able forms,  surmounted  by  a  brick  arch.  After  the  forms  are 
removed  the  surface  of  the  concrete,  inside  the  tunnel,  is  given 
a  J-inch  coat  of  mortar,  made  of  equal  parts,  by  volume,  of 
Portland  cement  and  sand,  and  troweled  smooth.  After  this 
mortar  has  set  and  dried  out,  it  is  covered  with  alternate  layers 
of  coal-tar  pitch  and  felt ;  seven  layers  of  pitch  and  six  of  felt. 
This  pitch  is  specified  as  "straight-run  coal-tar  pitch,  which 
will  soften  at  60°  Fahr."  The  pitch  is  mopped  onto 
the  surface  to  a  uniform  thickness  of  not  less  than  1-16  inch; 
and  the  felt  is  laid  immediately  on  this,  with  the  sheets  over- 
lapping not  less  than  12  inches  on  all  edges.  This  first  pitch- 
and-felt  lining  extends  from  the  bottom  to  a  point  about 
20°  30'  above  the  springing  line  of  the  tunnel. 

The  roof  of  the  tunnels  is  covered  with  two  triple  layers  of 
felt  and  seven  layers  of  pitch  laid  on  the  brickwork.  The 
triple  layers  are  made  up  as  above  described,  and  laid,  with  a 
lap  of  2  inches  to  6  inches,  on  a  bed  of  pitch  which  will  soften 
at  30°  Fahr.  With  the  second  triple-felt  layer  laid  in  a  similar 
manner,  these  waterproofing  courses  are  covered  with  one 
course  of  brick  laid  flat  in  |-inch  bed  of  mortar,  made  of  equal 
parts  of  cement  and  sand,  with  the  joints  completely  filled  with 
this  same  mortar. 

Engineers  have  also  found  the  following  method  of  water- 
proofing successful  for  arches,  abutments,  and  retaining  walls : 
For  a  first  coat,  asphalt  cut  with  naphtha  is  applied  as  a  paint 
to  the  concrete  surface  when  this  is  perfectly  dry.  Then  an 
asphaltic  mastic  is  applied,  made  of  i  part  asphalt  to  4  parts 
sand,  and  thoroughly  smoothed  with  hot  irons.  It  should  be 
observed  that  it  is  extremely  difficult  to  make  hot  asphalt  alone 
adhere  to  dry  concrete,  hence  the  use  of  the  naphtha.  The  cost 
of  the  waterproofing  here  described  ranges  from  10  to  20  cents 
per  square  foot  of  surface,  depending  upon  local  conditions. 

Hand  Auger  in  Prospecting   Work — Prospecting  work,    in 


TUNNEL    NOTES  245 

comparatively  soft  material,  is  sometimes  useful  in  arriving  at 
the  pitch  of  strata,  and  in  otherwise  determining  underground 
or  subaqueous  conditions.  In  a  paper  presented  to  the  Ameri- 
can Institute  of  Mining  Engineers,  Charles  Catlett,  M.  Am. 
Inst.  M.  E.,  describes  as  follows  the  set  of  tools  required  for  this 
work : 

1 i )  An  auger  bit  of  steel  or  Swede  iron,  with  a  steel  point 
twisted  into  a  spiral,  with  an  ultimate  diameter  of  2  inches  and 
an  ultimate  thickness  of  blade  of  not  less  than  J  inch.     The 
point  is  more  effective  when  split;  and  a  length  of  1 3  inches 
was  found  to  be  the  maximum  for  good  work.     The  1 3-inch 
auger  contains  four  turns;  and  this  is  welded  to  18  inches 
of  i -inch  wrought-iron  pipe,  with  screw-threads  for  connection. 

(2)  One  piece  of  if -inch  octagonal  steel,   12  inches  long, 
with  a  2-inch  cutting  edge.     This  is  also  welded  to  18  inches 
of  pipe,  with  thread  cut  for  connection. 

(3)  Teh  feet  of  i^-inch  iron  rod,  threaded  for  connection 
with  i -inch  pipe  at  one  end.     Connected  with  a  drill-bit,  this 
rod  is  used  as  a  jumper  in  starting  holes  in  hard  material.     It 
also  gives  additional  weight  to  the  drill  in  penetrating  rock. 

(4)  Section  of  i-inch  pipe  and  connections. 

(5)  An  iron  handle,  2  feet  long,  arranged  with  a  central  eye 
for  sliding  on  the  pipe,  and  a  set-screw  for  fastening  to  the 
pipe. 

(6)  A  sand-pump;  made  of  i  or  2  feet  of  i-inch  pipe,  with 
a  simple  leather  valve  and  a  cord  for  lifting  it. 

(7)  Two  pairs  of  pipe-tongs ;  or  two  monkey  wrenches,  with 
attachments  for  turning  them  into  pipe-tongs. 

(8)  Sundries :  Twenty-five  feet  of  tape,  oil  can,  flat  file, 
cheap  spring-balance,  water  bucket,  etc. 

The  auger  is  used  by  two  men  up  to  25  feet,  and  three  men 
to  35  feet;  for  borings  from  35  to  50  feet  deep  a  rough  frame 
or  trestle  is  required  for  the  third  man  to  stand  upon.  For 
borings  over  50  feet  it  is  generally  necessary  to  remove  one  or 
two  of  the  top  pipe  sections  when  the  auger  is  lifted. , 

In  drilling,  just  enough  water  is  continually  used  to  soften 
the  material.  In  hard  material  the  drill-bit  is  screwed  and 


246  MODERN    TUNNEL    PRACTICE 

worked  as  a  churn  drill.  With  either  the  auger  or  drill,  the 
material  extracted  is  washed,  and  a  sample  is  preserved  of  the 
stratum  penetrated.  After  washing  all  the  material  in  one 
stratum,  the  washed  material  is  mixed,  and  a  sample  is  put 
into  a  bottle  and  labeled.  An  accurate  record  of  the  borings  is 
essential;  and  to  this  end  the  foreman  is  instructed  to  write 
down  everything  in  a  small  notebook,  trusting  nothing  to 
memory. 

The  proper  classification  of  the  materials  obtained  from  a 
test-boring  of  any  kind  is  extremely  important,  if  these  tests 
are  to  be  of  any  real  use  to  a  prospective  bidder  upon  the  work. 
The  usual  method  is  to  specify  the  depth  of  the  individual 
sample,  as  measured  from  the  surface,  and  the  thickness  of  each 
stratum. 

Cases  occur  where  this  information  is  misleading,  especially 
where  the  classification  may  be  in  terms  not  plainly  understood 
by  the  bidder. 

It  has  been  suggested  with  some  force  that  a  better  classifi- 
cation is  one  adding  to  the  statement  of  general  depth  and 
thickness,  a  column  showing  the  time  consumed  in  penetrating 
the  several  strata.  This,  at  least,  would  be  a  close  physical 
classification ;  and  it  would  certainly  assist  in  arriving  at  a  more 
intelligent  conclusion.  It  costs  no  more  than  the  present 
method. 

It  is  well,  in  work  of  this  kind,  to  use  a  20- foot  hoisting  gin, 
equipped  with  a  6-inch  block  and  fall,  and  100  feet  of  f-inch 
rope.  A  Yale  &  Towne  |-ton  differential  chain  block  is  also 
very  useful  in  pulling  up  the  pipe. 

The  hoisting  gin  must  be  portable.  It  is  made  to  fold  up, 
and  is  used  as  a  platform  to  carry  the  pipes,  etc.,  lashed  to  it. 
This  gin  can  be  made  of  three  pieces  of  4  x  4-inch  spruce  tim- 
ber, each  20  feet  long.  The  top  of  each  piece  is  chamfered, 
and  a  bolt  is  inserted  to  prevent  splitting.  The  middle  piece 
is  chamfered  on  two  sides,  and  the  others  on  one  side  only. 
A  f-inch  bolt,  with  a  square  head  and  slot  with  pin  or  dowel, 
passes  through  the  three  sticks;  and  from  this  is  suspended  a 
f-inch  round  iron  "bail,"  with  a  "drop"  sufficient  to  permit 


TUNNEL    NOTES 


247 


it  to  pass  freely  over  the  top  of  the  middle  leg.  Cleats  nailed 
to  the  middle  leg  form  a  ladder. 

Tunnel  Cross-section  Instruments — Various  devices  are  used 
for  cross-sectioning  a  completed  rock  tunnel,  or  for  comparing 
the  actual  contour  of  the  tunnel  and  all  its  irregularities  with 
the  theoretical  or  contract  cross-section. 

In  the  new  Croton  Aqueduct  tunnel,  these  contours  were 
taken  every  10  feet  over  a  length  of  30  miles;  and  F.  W. 
Watkin,  M.  Am.  Soc.  C.  E.,  devised  an  instrument  which  was 
more  accurate  and  more  convenient  to  operate  than  the  older 
forms. 


FIG.  116. — Cross-section  Instrument  for  Tunnel  Work. 

The  circular  disk  was  3  feet  in  diameter,  and  it  was  attached 
to  a  vertical  iron  rod  which  slid  up  and  down  in  a  socket  and 
could  be  regulated  by  a  thumb-screw.  The  disk  and  rod  were 
supported  by  a  tripod  with  extension  legs. 

The  disk  was  set  at  right  angle  to  the  axis  of  the  tunnel,  and 
its  center  was  raised  to  coincide  with  the  tunnel  center.  Cross- 
sections  were  then  taken  with  a  light,  graduated  rod,  and  the 
measurements  would  show  at  once  if  any  trimming  were 
necessary. 


MODERN    TUNNEL    PRACTICE 

About  the  same  time  Alfred  Craven,  M.  Am.  Soc.  C.  E.,  de- 
vised the  instrument  illustrated  in  Fig.  116,  which  is  more 
portable  than  the  other.  The  circular  disk  was  18  inches  in. 
diameter,  and  was  attached  to  a  vertical  brass  tube  mounted 
on  a  shifting  top,  ball-and-socket  joint,  and  leveling  screw 
tripod  head.  The  disk  was  graduated  from  o  at  the  top  to 
1 80°  at  the  bottom,  for  each  degree  of  the  circle.  A  hardwood 
arm  or  rest  revolved  on  a  central  pin  on  the  face  of  the  disk. 


FIG.  117. — Plummet-lamp  for  Tunnel  Work. 

On  this  was  placed  a  wooden  measuring  rod,  14  feet  long, 
tapering  from  2  inches  to  -J  inch,  and  graduated  for  feet  and 
tenths  from  the  small  end.  This  rod,  resting  on  the  arm,  was 
slid  out  to  touch  the  rock  at  any  point,  indicating  the  radial 
distance  from  the  center  line  and  the  angle  from  the  vertical. 
The  disk  must  be  at  right  angle  with  the  axis  of  the  tunnel ; 
and  to  insure  this  a  small  sighting  tube  was  attached  to  it,  in 


TUNNEL    NOTES  249 

line  with  the  tunnel  axis,  and  set  on  a  distant  line  light.  The 
elevation  of  the  center  of  the  disk  was  taken  before  the  cross- 
section  was  measured. 

From  15  to  20  measurements  usually  covered  all  prominent 
irregularities  at  any  one  station.  These  were  recorded  like 
ordinary  cross-section  notes.  The  disk  diagrams  were  plotted 
in  the  office  by  using  a  3-inch  German  silver  circular  protractor, 
graduated  both  ways  from  o  to  180°,  and  provided  with  a  horn 
center.  A  graduated  metal  arm  swings  about  the  center  and 
marks  the  distances  out.  The  areas  were  generally  measured 
by  a  polar  planimeter. 

v  Plummet-lamp — The  plummet-lamp  was  first  introduced  by 
the  late  Eckley  B.  Coxe,  especially  for  use  in  mine  surveying. 

As  shown  in  the  illustration,  a  large  brass  plummet  is  hol- 
lowed out  in  the  upper  part,  as  a  receptacle  for  oil,  and  this 
is  fitted  with  a  wick,  placed  in  the  axis  of  the  plummet.  This 
plummet  is  suspended  by  two  chains  attached  to  a  compensat- 
ing ring,  connected  with  the  plummet  by  two  small  screws  with 
conical  points. 

When  required,  these  lamps  are  fitted  with  a  safety,  or  fire- 
damp attachment,  resembling  that  used  with  the  Mueseler 
lamp. 

In  use,  these  lamps  are  suspended  from  screw-eyes  driven 
into  a  wooden  plug  in  a  hole  drilled  in  the  roof  of  the  tunnel. 
The  string  is  tied  to  the  screw-eye  and  placed  in  exact  line, 
and  left  there;  whenever  a  line-sight  is  wanted  the  plummet- 
lamp  is  attached  to  the  string.  At  the  present  time  various 
forms  of  these  plummet-lamps  are  furnished  by  instrument 
makers. 


CHAPTER     XIV 

THE   CONSTRUCTION    OF   THE   SIMPLON   TUNNEL 

Water- works  tunnel  at  Cincinnati : — Telephone  and  freight  transportation 
tunnels  in  Chicago. 

The  following  description  of  the  longest  of  the  Alpine  tun- 
nels is  taken  from  a  contribution  to  Engineering  News*  made 
by  Mr.  C.  R.  King,  who  visited  and  carefully  studied  the  work 
in  progress.  Mr.  King's  story  of  the  history  of  the  enterprise, 
and  its  importance  as. a  link  in  railway  transportation  in  South- 
ern Europe,  has  been  somewhat  condensed. 

Much  of  the  matter  here  described  would  fall  under  various 
chapter  heads.  But  it  has  been  deemed  better  to  present  it  in 
this  place  consecutively  and  together,  as  better  illustrating 
what  may  be  termed  the  latest  tunnel  practice  among  Euro- 
pean engineers.  The  same  remark  applies  to  the  other  two. 
articles  coming  under  this  chapter  head. 

Simplon  Tunnel. — The  Simplon  Pass  is  one  of  the  most  noted 
of  the  Alpine  passes,  and  the  Simplon  Pass  road  was  built  in 
1806  by  Napoleon.  Projects  for  tunneling  the  pass  have  been 
many.  In  1857  Mr.  Clo-Venetz  proposed  a  high-level  tunnel, 
7.5  miles  long;  and,  in  1860,  the  French  engineer,  Vauthier, 
planned  a  tunnel  11.3  miles  long,  or  the  first  of  the  low-level 
projects.  The  Simplon  Company,  organized  in  1875,  gathered 
together  much  data  of  value  to  the  proposed  work;  and  in  1893 
the  Jura-Simplon  Railway  Company  entered  into  a  contract 
with  Brandt,  Brandau  &  Co.,  of  Winterthur,  Switzerland,  to 
construct  a  tunnel  from  Brieg,  on  the  north  side,  to  Iselle,  on 
the  Italian  side  of  the  Simplon  Pass.  The  general  route  of 
this  tunnel  is  shown  in  the  accompanying  map ;  and  it  is  prac- 
tically the  same  as  that  laid  down,  in  1875,  for  the  old  Simplon 

*For  the  complete  article  see  Engineering  News,  August- September,  1903. 

250 


THE  CONSTRUCTION   OF  THE  SIMPLON  TUNNEL 

Company,  by  Mr.  Louis  Favre,  the  contractor  for  the  St.  Goth- 
ard tunnel. 

The  plans  were  finally  approved  in  their  engineering  fea- 
tures by  a  commission  of  noted  engineers ;  and  by  the  treaty 
of  Nov.  25,  1895,  between  the  Italian  and  Swiss  governments, 
the  Jura-Simplon  Railway  Company  was  permitted  to  construct 
and  operate  the  tunnel  line  lying  between  Brieg  and  Domo 
d'Ossola. 

The  Simplon  tunnel  line  cuts  the  territory  lying  between 
the  St.  Gothard  and  the  Mont  Cenis  tunnels.  Its  construction 
will  especially  benefit  the  Paris,  Lyons  &  Mediterranean,  the 


1st  Project-  (1882) 


FIG.  118. — Simplon  Tunnel:  Map  Showing  Various  Routes  from  1832 

to   1893. 

Jura-Simplon  and  the  Italian  Mediterranean  railway  compan- 
ies ;  and  the  territory  best  served  by  it  will  be  French  Switzer- 
land and  northeastern  Italy,  or  Piedmont  and  Lombardy.  It 
will  save  from  3^  to  5  hours  in  time  of  transit  between  Paris 
and  Milan,  and  shorten  the  London-Brindisi  route  about  180 
miles. 

As  the  Italian  railway  system  ended  at  Domo  d'Ossola,  some 
miles  south  of  the  tunnel  terminus  at  Iselle,  the  Italian  govern- 
ment contracted,  in  the  treaty  of  1895,  to  build  the  connecting 
line  between  these  points,  as  shown  on  the  map.  The  Italian 
government  is  also  building  a  new  line  from  Milan  to  Domo 
d'Ossola.  This  new  railway  includes  various  features  of  en- 


252 


MODERN    TUNNEL    PRACTICE 


gineering  interest,  and  some  of  its  more  important  works  are 
here  noted. 

The  new  line  from  Milan  starts  at  Gallarate,  on  the  existing 
line,  and  follows  the  west  shore  of  Lake  Maggiore,  and  thence 
proceeds  directly  north  to  Domo  d'Ossola  and  Iselle.  The 
grades  have  been  much  reduced.  While  the  grades  of  the  exist- 
ing line  are  i%,  and  occasionally  1.6%,  those  on  the  new  line 
do  not  exceed  0.6%.  The  tunnel  at  Farragiana  is  one  of  the 
most  notable  works  on  the  Arona-Domo  d'Ossola  section, 
though  there  are  many  small  tunnels.  This  tunnel  is  12,000 
feet  long,  and  penetrates  a  very  hard  porphyric  rock.  The 
new  line  saves  1 1  miles  in  distance  between  Milan  and  Domo 


FIG.  119.— Profiles  of  Existing  and  Proposed  Railways  at  the  Italian  End 
of  the  Simplon  Tunnel. 

cT'Ossola;  and,  with  its  improved  gradients,  greater  loads  and 
higher  speeds  will  be  possible. 

The  Domo  d'Ossola-Iselle  section,  1 1^  miles  long,  is  built 
through  a  region  of  extremely  diversified  topography,  necessi- 
tating numerous  tunnels  and  stone  arch  bridges,  viaducts,  etc. 
The  maximum  gradient  is  2%%,  and  the  longest  tunnel,  at 
Trasquera,  is  5,656  feet  long.  The  seven  tunnels  on  this  u£ 
miles  aggregate  in  length  over  4  miles. 

The  Working  Plant  and  Its  Accessories. — The  contract  time 
for  constructing  the  Simplon  tunnel,  12.4  miles  long,  was  five 
and  a  half  years,  and  the  course  of  events  has  shown  that  this 
allotted 'time  was  none  too  long.  To  carry  on  a  work  whose 


THE   CONSTRUCTION   OF  THE  SIMPLON  TUNNEL  253 

duration  was  half  a  decade,  the  two  parts  of  which  were  sepa- 
rated by  a  dozen  miles,  and  the  whole  of  which  was  located 
far  from  the  nearest  centers  of  mechanical  industry,  obviously 
necessitated  a  working  plant  of  unusual  dimensions.  This 
working  plant  had,  moreover,  to  be  divided  into  two  separate 
plants,  one  at  each  end  of  the  tunnel,  each  independent  of  the 
other  and  complete  in  itself.  Each  plant  had  to  supply  power 
to  provide  means  for  ventilation,  illumination,  air  refrigera- 
tion, drainage  and  transportation  service.  For  each  plant  there 
had  also  to  be  workshops  in  which  machinery  and  tools  could 
be  repaired.  There  had  then  to  be  provided  houses  for  the 
workmen  and  engineers,  water  supply,  hospital  service,  sani- 
tary conveniences,  stores  for  provisions  and  materials,  and  a 
multitude  of  minor  necessities. 

The  two  plants  at  the  opposite  ends  of  the  tunnel  are,  as 
nearly  as  possible,  duplicates.  At  the  Swiss  end  the  entrance 
is  located  2  miles  east  of  Brieg,  at  685.7m.  (2,246  feet)  alti- 
tude, beneath  the  hills  rising  from  the  bank  of  the  River  Rhone, 
and  on  this  narrow  and  level  bank  the  working  plant  is  laid 
out  with  great  uniformity.  At  the  Italian  end  the  plant  is 
located  in  the  deep  valley,  or  the  Val  Verde,  at  the  upper  end 
of  which  are  the  tunnel  entrances;  and  the  topographical  con- 
ditions here  are  such  as  to  prevent  a  regular  layout.  The  fol- 
lowing description  of  the  various  installations  of  the  working 
plant  applies, -with  very  few  exceptions,  to  both  the  Swiss  and 
Italian  ends;  but  the  specific  structures  described  are  those  at 
the  Italian  end,  unless  otherwise  stated.  For  the  sake  of  con- 
venience, the  description  is  divided  under  the  following  heads : 
Power  Installations ;  Ventilation ;  Air  Refrigeration  ;  Illumina- 
tion; Drainage;  Workshops;  Buildings  and  Accessories; 
Transportation  Service. 

Power  Installations — Water  power  is  employed  for  prac- 
tically all  purposes  at  both  ends  of  the  tunnel.  At  the  Swiss 
end,  about  2\  miles  upstream  from  the  tunnel  entrance,  the 
River  Rhone  is  dammed,  and  the  water  collected  into  a  num- 
ber of  reservoirs,  provided  with  necessary  gates  for  controlling 
the  inflow  and  outflow.  From  these  reservoirs  the  water  is 


254  MODERN    TUNNEL    PRACTICE 

conveyed  for  about  two  miles  in  a  reinforced  cement  flume. 
This  flume  crosses  a  flat  and  well-cultivated  plain ;  at  the  point 
where  this  plain  drops  steeply  to  the  Rhone  valley  the  conduit 
changes  from  rectangular  flume  to  two  cast-iron  pipe  lines  in 
trench,  which  reach  to  the  power  house,  a  distance  of  about 
one-half  mile.  An  air  inlet  pipe  located  at  the  brow  of  the  hill 
serves  both  penstocks.  The  total  power  available  from  this 
service  is  2,200  horse-power. 

At  the  Italian  end  the  power  is  derived  from  the  Diveria, 
about  2^  miles  above  the  works,  and  near  Gondo,  the  last 
village  in  Swiss  territory.  Here  the  river  is  dammed  and  the 
water  collected  into  a  forebay  8om.  (262.5  feet)  long,  from 
which  it  is  admitted  into  a  delivery  reservoir  having  a  super- 
ficial area  of  270  square  m.  and  a  depth  of  2-Jm.  (8.2  feet). 
At  the  lower  ends  of  these  reservoirs  there  are  overflow  weirs, 
washout  sluices,  and  the  regulating  gates  for  controlling  the 
.supply  to  the  penstocks. 

From  the  gate  house  the  penstock,  for  a  distance  of  i,3OOm. 
(4,265  feet),  is  carried  along  underneath  the  Simplon  road, 
and  consists  of  cast-iron  pipe  Qocm.  (2.95  feet)  in  diameter, 
built  in  6m.  (19.68  feet)  lengths,  with  shells  i  inch  thick,  each 
weighing  4,400  pounds.  This  pipe  was  furnished  by  W.  Boss- 
hardt,  of  Zurich,  Switzerland.  Near  Paglinp,  and  about  24m. 
(78.74  feet)  before  the  termination  of  the  cast-iron  pipe  line, 
there  is  an  escape  pipe,  with  an  adjustable  disk  cover,  designed 
to  reduce  the  pressure  from  118  pounds  to  103  pounds  per 
square  inch.  This  escape  pipe  was  continually  bursting  under 
the  water  pressure. 

At  the  end  of  the  first  i,3OOm.  (4,265  feet)  the  cast-iron 
penstock  is  replaced  by  one  of  wrought-iron  pipe  of  the  same 
diameter.  This  wrought-iron  penstock  continues  to  the  power 
plant,  2,840m.  (9,317  feet),  and  has  |-inch  shell.  It  was  sup- 
plied by  Rieter  &  Co.,  of  Winterthur,  Switzerland.  This  pipe 
line  is  carried  along  against  the  wall  which  retains  the  Simplon 
road,  being  supported  on  granite  piers,  and  enveloped  in  a  sort 
of  matting,  which  serves,  in  a  degree,  to  protect  the  metal  from 
variations  in  temperature.  A  little  above  Iselle  the  pipe  line  is 


THE  CONSTRUCTION  OF  THE  SIMPLON  TUNNEL  255 

carried  across  the  Diveria  by  a  suspension  cable.  Further  on 
a  jutting  bluff  is  penetrated  by  a  tunnel  282m.  (925  feet)  long1. 
Here,  also,  the  penstock  is  enlarged  to  a  diameter  of  im.  (3.28 
feet)  for  a  length  of  i8i.7m.  (596  feet)  above  the  power- 
house turbines.  The  total  head  of  water  on  these  turbines  Is 
I7om.  (558  feet),  but  the  turbines  of  the  ventilation  house 
further  upstream  work  under  lorn.  (32.8  feet)  less  head.  It 
should  be  noted  also  that  pressure  at  the  power-house  turbines 
can  be  varied  from  13  to  17  atmospheres  by  means  of  the 
escape  valve  at  Paglino,  previously  described.  Just  before 
reaching  the  power  station  the  pipe  line  again  crosses  the  Di- 
veria, this  time  on  a  double-deck  bridge.  This  bridge  also 
serves  to  connect  the  high  road  with  the  station,  and  for  the 
carriage  of  materials  between  the  works  on  the  opposite  banks 
of  the  river.  It  was  constructed  by  the  Societa  Nazionale  delle 
Officine  di  Savigliano,  of  Turin,  Italy. 

The  power  house  contains  three  Pelton  wheels,  furnished  by 
the  well-known  firm  of  Escher,  Wyss  &  Co.,  of  Zurich,  Switz- 
erland, two  being  250  h.-p.  each,  and  one  of  600  h.-p.  All 
three  wheels  are  horizontal,  and  run  at  170  revolutions  per 
minute.  They  operate  the  pressure  pumps  to  accumulators  sup- 
plying water  to  the  rock  drills.  There  are  five  of  these  pumps, 
the  first  four  being  operated  by  the  two  250  h.-p.  turbines,  and 
the  fifth  by  the  600  h.-p.  turbine.  The  transmission  shafting 
from  the  turbines  to  the  pumps  is  so  designed  that  any  one 
of  the  ten  pumps  can  be  thrown  out  of  connection  at  will.  They 
are  geared  directly  to  the  water-wheel  shaft,  and  are  thrown 
into  and  out  of  connection  by  a  sliding  spur  wheel  on  the  pump 
shaft.  Three  of  the  pumps  have  plunger  diameters  of  48mm. 
and  68mm.,  with  66omm.  stroke,  and,  at  78  revolutions,  fur- 
nish 6  liters  of  water  per  second.  The  remaining  two  pumps 
have  plunger  diameters  of  6omm.  and  85mm.,  and  a  stroke  of 
im.;  and  they  discharge  12  liters  of  water  per  second  at  65 
revolutions.  The  highest  pressure  of  water  possible  with  these 
pumps  is  1 20  atmospheres  per  square  centimeter. 

The  water  for  the  pumps  is  taken  from  two  sources.  The 
first  is  an  8-inch  pipe  connection  with  the  penstock,  and  the 


256  MODERN    TUNNEL    PRACTICE 

second  is  the  Rovale  torrent,  on  the  heights  above  the  portals  of 
the  tunnel.  The  Rovale  water  is  used  for  the  pumps  so  long 
as  the  quantity  supplied  is  sufficient,  but  in  times  of  shortage 
resource  is  had  to  the  penstock  supply.  In  both  cases  the  water 
is  cleaned  of  all  sediment  by  being  passed  through  filter  beds 
before  being  delivered  to  the  pumps. 

This  battery  of  pumps  is  calculated  for  a  capacity  of  40 
liters  per  second  at  a  pressure  of  from  40  to  120  atmospheres 
(64  gallons  per  minute  at  1,175  pounds  per  square  inch)  ;  but 
the  present  average  supply,  which  suffices  for  the  drills,  in- 
jectors, etc.,  is  20  liters  per  second  at  90  atmospheres  per  centi- 
meter. It  may  be  mentioned  here  that  the  quantity  of  water 
used  in  each  drill  cylinder  is  One  liter  per  second ;  and  as  there 
are  two  cylinders  to  each  boring  head,  and  three  heads  for 
each  point  of  advance,  and  never  more  than  three  points  of 
advance,  we  have  i  X2X3  X  3  =  18  liters  required  for  three 
headings.  With  a  pressure  at  the  accumulators  of  from  80 
to  100  atmospheres,  the  pressure  at  the  drills,  6  kilometers  dis- 
tant, is  from  60  to  80  atmospheres.  The  pressure  pipe  to  the 
drills  is  loomm.  in  diameter,  with  a  shell  4mm.  thick,  and  was 
tested  before  installation  up  to  250  atmospheres.  This  pipe 
was  supplied  by  the  Mannesmann  Tube  Works,  of  Remscheid, 
Germany. 

In  the  same  room  with  the  pumps  are  two  air  compressors. 
One  of  these  is  a  duplex  Burckhardt  compressor,  with  a  capac- 
ity of  2  cubic  m.  of  free  air  per  minute,  built  by  the  Masch- 
inenfabrik  Burckhardt,  of  Basle,  Switzerland;  and  the  other 
is  an  Ingersoll-Sargent  compressor,  with  a  capacity  of  3  cubic 
m.  of  free  air  per  minute,  built  by  the  Ingersoll-Sargent  Rock 
Drill  Company,  of  New  York  City.  These  two  compressors 
pump  to  a  receiver  consisting  of  Mannesmann  tubes  in  rows, 
inclined  in  the  form  of  a  V  above  a  cement-lined  pit  to  allow  of 
their  drainage.  The  pressure  carried  is  from  70  to  80  atmos- 
pheres per  square  cm.  From  the  receiver  the  air  is  piped  to 
various  points  about  the  works,  and  into  the  tunnel  to  about  the 
fifth  kilometer,* to  supply  the  compressed-air  locomotives. 

Besides  the  three  water  wheels  in  the  main  power  house,  the 


THE  CONSTRUCTION  OF  THE  SIMPLON  TUNNEL 


257 


water-power  described  supplies  two  turbines  in  the  venti- 
lator house  and  one  in  the  lighting  plant.  The  maximum 
power  supplied,  and  its  distribution,  is  about  as  follows :  For 
high-pressure  pumps,  700  h.-p. ;  for  air  compressors,  400  h.-pu.; 
for  ventilation,  500  h.-p. ;  for  illumination,  100  h.-p. ;  for  shop 
machines,  100  h.-p.;  total,  1,800  h.-p.  It  is  expected  that  as 
the  work  progresses  another  large  turbine  and  additional  high- 
pressure  pumps  will  be  installed. 

Besides  the  hydraulic  power  plant  described  above,  there  is 


Sectional        Plan        of       Tunnels. 

FIG.  120.— Ventilating  Plant  at  Swiss  End  of  Tunnel,  and  Section  of  Tun- 
nel Showing  Water-pipes. 

at  the  Italian  end  a  supplementary  steam-power  plant  avail- 
able as  a  reserve  source  of  power.  This  plant  is  located  in  a 
building  joining  the  main  power  house,  and  consists  of  three 
compound  engines,  two  of  80  h.-p.  each  and  one  of  60  h.-p. 
The  engine  and  boiler  in  each  case  are  combined  on  a  single 
bed  plate.  These  machines  were  transported  to  the  works  over 
the  highroads,  using  40  and  50  horse  teams. 

Ventilation — For  ventilating  the  tunnel  during  construction, 
and  after  it  is  put  in  operation,  a  permanent  ventilating  plant 
has  been  installed  at  each  end,  as  shown  in  Fig.  120.  The 


258 


MODERN    TUNNEL    PRACTICE 


ventilating  machinery  at  each  end  consists  of  two  200  h.-p. 
turbines,  running  at  400  revolutions  per  minute,  and  driving 
two  fans  3.75m.  (12.3  feet)  in  diameter.  The  turbines  were 
supplied  by  Escher,  Wyss  &  Co.,  and  the  fans  by  Sulzer  Bros., 


to  Heading  Tunnel  No.  I.  to  I  set  I e 


FIG.  121. — Sketch-plan  Showing  Passages  for  Delivering  Air  from  Fans  to 
Tunnel,  at  the  Italian  End. 

of  Winterthur.  This  machinery  is  arranged  differently  at  the 
two  ends.  At  the  Swiss  end  the  fans  are  placed  one  above  the 
other,  close  to  the  portal,  and  the  air  passage  is  carried  across 
the  roof  of  the  tunnel.  At  the  Italian  enti  of  the  tunnel  the 


THE  CONSTRUCTION  OF  THE  SIMPLON  TUNNEL  259 

fans  are  arranged  one  behind  the  other,  and  some  distance 
away  in  a  ventilator  house,  from  which  an  air  passage  leads  to 
the  tunnel,  as  shown  in  Fig.  121.  The  ventilators  at  each  end 
will  furnish  50  cubic  m.  of  air  per  second,  at  a  gage  pressure 
of  25omm.  of  water,  when  running  in  parallel ;  and  25  cubic  m. 
of  air  at  a  pressure  of  5oomm.  of  water,  when  running  in 
series  in  a  tunnel  10  kilometers  long  and  8  square  m.  sectional 
area. 

Turning  to  Fig.  121,  it  will  be  seen  that  the  air  passage  from 
the  ventilator  house  bifurcates  near  its  tunnel  end,  and  one 
fork  goes  to  each  tunnel.  A  door  at  the  angle  of  the  bifurca- 
tion closes  either  fork  of  the  passage  at  will.  Sail-cloth  cur- 
tains close  the  portals  of  the  tunnel,  and  are  operated  either 
by  hand  or  by  electric  motors.  It  will  readily  be  seen  from 
the  plans  that  the  air  can  be  circulated  either  in  Tunnel  I  or 
Tunnel  2,  as  desired;  its  movement  being  accomplished  either 
by  compression  or  aspiration. 

The  foregoing  remarks  have  referred  to  the  ventilation  of 
the  tunnel  after  completion.  To  ventilate  the  workings  dur- 
ing construction  there  is  a  branch  from  the  air  passage  (Fig. 
12 1 )  to  the  service  gallery,  opened  up  along  the  line  of  Tun- 
nel 2.  If  the  ventilation  is  by  compression,  the  air  passes  along 
Gallery  2  to  the  last  cross-passage,  through  this,  and  then  along 
Tunnel  i,  as  shown  by  the  arrows  in  the  sketch  (Fig.  122). 
If  the  ventilation  is  by  aspiration,  then,  of  course,  the  flow  of 
the  air  tunnel  is  in  the  opposite  direction. 


FIG.  122.— Diagram  Showing  Circulation  of  Air  in  Tunnel. 

At  this  point  it  may  be  well  to  note,  in  explanation  of  Fig. 
122,  that  it  shows  diagrammatically  the  condition  of  work 
from  the  Italian  end  in  July,  1902.  At  this  time  the  working 
face  of  Tunnel  I  was  some  soom.  (1,640  feet)  ahead  of 


260  MODERN    TUNNEL    PRACTICE 

that  of  Tunnel  2,  owing  to  the  fact  that  work  had  been  stopped 
in  the  latter  passage  by,  treacherous  material  at  meter  4490. 
To  pass  this  material,  side  passage  No.  22  had  been  bored,  and 
excavation  from  it  back  to  the  treacherous  material  had  been 
begun.  This  work  will  again  be  referred  to  in  more  detail ; 
but  its  importance  at  this  point  lies  in  the  fact  that  it  inter- 
rupted the  route  of  air  circulation  described  above.  Conse- 
quently, a  small  fan  was  placed  at  cross-passage  21  B,  and 
forced  air  through  a  1 4-inch  pipe  to  the  working  force  of  Tun- 
nel i.  In  conclusion,  it  should  perhaps  be  noted  that  all  side 
passages  are  sealed  up  as  the  work  advances,  to  prevent  short- 
circuiting  of  the  air  current. 

At  present  the  ventilating  potential  of  the  plant  is  much  in 
excess  of  the  actual  needs.  One  fan  operating  so  as  to  give  a 
gage  pressure  of  6omm.  of  water,  gives  i  cubic  m.  of  fresh  air 
per  second  at  the  working  face.  This  circulation  causes  no 
unpleasant  draft;  but  by  increasing  the  gage  pressure  to 
loomm.  of  water,  the  miners'  lamps  used  by  the  workmen  are 
blown  out.  The  turbines  and  fans  are  worked  alternately,  and 
twelve  hours  each.  It  is  customary  to  lay  the  dust  and  to  re- 
freshen the  air  entering  the  fans  by  occasionally  flooding  the 
sides  of  the  passages  with  water.  The  penstock  for  the  venti- 
lator turbines  is  a  branch  from  the  main  penstock  near  the 
two-deck  service  bridges,  previously  mentioned. 

Previous  to  the  installation,  of  the  hydraulic  plant,  a  steam 
ventilating  plant  was  installed  at  a  point  near  the  main  venti- 
lator house.  This  consisted  of  a  10  h.-p.  engine  running  a 
fan  delivering  air  through  Tunnel  2,  by  a  pipe  5ocm.  in  di- 
ameter. At  1,200  revolutions  per  minute  this  fan  furnishes 
2  cubic  m.  of  air  per  second,  with  a  gage  pressure  of  lomm. 
of  water.  In  case  of  accident  to  the  main  plant,  this  small 
steam  plant  would  supply  enough  air  to  prevent  the  stoppage 
of  work,  and  it  is  consequently  kept  in. readiness  as  a  reserve 
plant  for  ventilation. 

Air  Refrigeration — Before  commencing  the  work,  the  ele- 
vation of  temperature  due  to  the  heat  of  the  rock  was  estimated 
as  i°  Cent,  for  every  44m.  (144  feet)  of  subterranean  advance; 


THE  CONSTRUCTION  OF  THE  SIMPLON  TUNNEL          26l 

but  the  actual  temperatures  encountered,  owing  to  different  in- 
fluences, have  differed  materially  from  those  estimated.  At 
the  Italian  side  the  great  flood  of  water  coming  into  the  tunnel 
was  at  first  sufficient  to  keep  the  air  cool ;  but  as  the  work  pro- 
gressed beyond  the  leaks  it  became  necessary  to  resort  to  arti- 
ficial means  for  cooling  the  workings.  At  the  Swiss  side,  on 
the  contrary,  it  has  been  from  the  first  a  matter  of  some  diffi- 
culty to  keep  the  air  cool  enough  for  comfort,  since  the  in- 
filtration of  water  has  been  too  small  to  have  any  appreciable 
effect.  It  should  be  emphasized,  however,  that  the  excessive 
temperatures  which  have  been  frequently  recorded  in  the  news- 
papers have  no  substance  in  fact.  The  highest  temperature 
which  has  been  encountered  in  the  tunnel  workings  is  55°  Cent., 
and  was  encountered  during  the  autumn  of  1902.  at  about  the 
eighth  kilometer  from  the  Swiss  end.  As  work  progresses  the 
temperature  appears  to  be  gradually  decreasing. 

The  method  of  refrigerating  the  air  is  practically  the  same  at 
both  ends ;  cold  water  is  forced  into  the  -headings  and  there 
broken  into  spray.  At  the  Swiss  end  the  refrigerating  water  is 
pumped  from  the  River  Rhone  and  forced  through  a  I  Cl- 
inch pipe  laid  along  one  side  of  Tunnel  No.  2.  This  pipe  is 
insulated  by  jacketing  it  with  a  pipe  15!  inches  in  diameter  and 
filling  the  annular  space  with  charcoal.  With  this  insulation 
the  rise  in  temperature  due  to  the  passage  of  water  through  9 
kilometers  of  pipe  is  only  3°C.  In  Fig.  120  is  shown  a  trans- 
verse section  of  Tunnel  No.  2,  with  the  location  of  the  refriger- 
ating water  pipe  and  also  that  of  the  high-pressure  pipes  sup- 
plying water  to  the  rotary  drills.  At  the  Italian  end  the  cool- 
ing water  is  taken  from  one  of  the  springs  encountered  in  the 
tunnel,  as  shown  in  Fig.  121. 

Illumination — For  lighting  the  interior  of  the  tunnel  gas  is 
used  at  the  north  end,  while  at  the  south  end,  far  from  any  gas 
works,  each  miner  carries  his  own  oil  lamp.  To  the  American, 
engineer  this  crude  method  of  lighting  is  a  matter  of  some 
surprise,  considering  the  necessity  for  ventilation  and  the  fact 
that  there  is  an  electric  light  plant  at  each  end  for  lighting  the 
buildings  and  yards.  At  the  Italian  end  the  central  station  is 


262  MODERN    TUNNEL    PRACTICE 

located  near  the  main  power  house.  There  are  here  two  genera- 
tors, one  supplying  power  to  32  5oo-candle-power  arc  lamps  for 
lighting  the  yards,  and  one  supplying  300  incandescent  lamps 
of  10,  1 6  arid  32-candle-power.  These  generators  were  sup- 
plied by  J.  J.  Rieter  &  Co.,  of  Winterthur,  Switzerland,  and  are 
run  by  a  no  horse-power  turbine  supplied  by  the  Societe  de 
Constructions  Mecaniques,  of  Vevay,  Switzerland.  There  is 
also  a  reserve  dynamo  operated  by  shafting  from  the  reserve 
steam-power  plant  previously  described.  This  is  a  i6-kw. 
dynamo,  supplied  by  the  Compagnie  de  ITndustrie  Electrique, 
of  Secheron,  near  Geneva,  and  it  supplies  ten  5OO-candle- 
power  arc  lamps  and  100  i6-candle-power  incandescent 
lamps. 

Drainage — The  drainage  of  the  tunnel  works  is  effected  by 
gravity,  excepting  for  a  length  of  5Oom.  in  the  center  of  the 
tunnel.  At  the  Swiss  end  the  fall  is  0.2%  for  9,1 84m.,  and  at 
the  Italian  end  it  is  0.7%  for  io,o86m.  The  flow  of  water 
measured  at  the  Swiss  end  at  the  last  of  October,  1902,  was 
only  2,400  liters  per  minute,  and  at  the  Italian  end  it  was 
62,940  liters  per  minute,  with  a  temperature  in  summer  of 
I2°C.  At  the  Swiss  end  the  water  passes  into  a  special  drain 
excavated  in  the  floor  of  Tunnel  2,  but  at  the  Italian  end 
the  whole  floor  of  this  passageway  is  submerged  by  the  flood  of 
outgoing  water.  Without  this  auxiliary  passage  having  been 
excavated,  construction  at  the  Italian  end  would  have  been  very 
difficult,  if  not  impossible.  Indeed,  the  engineers  of  this  encj 
of  the  work  are  frank  in  stating  that  they  consider  that  for  any 
mountain  tunnel  of  importance,  say  over  six  miles  in  length, 
this  method  of  parallel  tunnel  construction  is  advisable  for 
several  reasons. 

Almost  all  of  the  water  at  the  Italian  end  is  encountered  be- 
tween meters  4000  and  4600.  In  this  distance  several  fissures 
discharge  streams  varying  from  5  liters  per  second  to  425  liters 
per  second.  The  largest  of  these  is  an  upright  elliptical  fissure 
about  4  feet  above  the  floor  of  the  cross-passage  21  B,  Fig.  122, 
and  the  amount  of  flow  from  it  is  13,500  liters  per  minute. 

Workshops. — The  main  machine  shops  for  the  repairs  of  rock 


THE  CONSTRUCTION  OF  THE  SIMPLON  TUNNEL  263 

drills  and  other  machines  requiring  accurate  work  are  built  in 
line  with  and  adjoining  the  power  station.  The  machine-tool 
equipment  consists  of  7  lathes,  7  milling  machines,  3  drills,  2 
cold  metal  saws,  2  screw  milling  machines,  and  a  planer,  a 
punch  and  a  plate  shear,  all  operated  by  a  small  turbine  with  a 
small  stationary  steam  engine  held  in  reserve.  In  addition  to 
these  general  tools,  one  end  of  the  shop  is  equipped  with  two 
testing  stalls  for  the  Brandt  rotary  drills  employed  in  the  tun- 
nel. In  these  stalls  the  drills  are  mounted  and  tested  on  blocks 
of  rock. 

Detached  from  the  main  building  are  a  number  of  smaller 
shops  for  various  purposes.  The  first  of  these  is  used  for  erect- 
ing the  heavy  steel  and  timber  bracing  frames  employed  in  cer- 
tain portions  of  the  tunnel,  as  will  be  described  in  a  succeeding 
division.  A  woodworking  and  carpenter  shop  adjoins  the 
frame  erecting  shop,  the  principal  work  done  here  consisting  of 
repairs  to  the  wooden  spoil  cars.  The  iron  cars  are  also  patched 
up  here.  Nearby  is  a  locomotive  roundhouse  with  stalls  for 
four  engines,  track  pits,  filters,  benches,  etc. 

Further  down  the  valley  are  sawmills  and  an  extensive  lum- 
ber yard.  Here  the  dressed  timber  for  special  tunnel  timbering 
is  cut  and  stored.  The  consumption  of  wood  in  the  tunnel  is 
very  great,  and  the  logs  from  which  it  is  cut  are  felled  in  the 
forests  which  cover  the  precipitous  mountain  sides  above  Iselle 
and  transported  to  the  sawmills  by  an  aerial  ropeway.  The 
waste  timber  from  the  working  is  used  for  fuel.  Near  the  lum- 
ber yard  there  is  a  storage  yard  for  the  cut  stone  for  the  tun- 
nel lining,  and  concrete  blocks  for  the  same  purpose  are  made 
in  a  building  located  on  the  opposite  bank  of  the  river,  at  the 
foot  of  the  spoil  bank  of  rock  taken  from  the  tunnel.  The  con- 
crete blocks  are,  however,  employed  only  in  special  cases,  as 
their  manufacture  is  more  costly  than  the  production  of  cut 
stone,  the  rough  blocks  for  which  are  received  from  the  spoil 
bank  or  from  the  quarries  near  Iselle,  to  which  a  track  is  built. 

One  of  the  most  important  buildings  of  the  plant  is  the  foun- 
dry and  blacksmith  shop.  The  foundry  is  equipped  for  founding 
the  iron  and  bronze  parts  of  the  rock  drills  and  such  other  small 


264  MODERN    TUNNEL    PRACTICE 

castings  as  are  required  in  case  of  emergency.  At  the  black- 
smith shop  the  cutter  heads  and  hand  drills  are  sharpened  at 
the  rate  of  several  thousand  a  day. 

Buildings  and  Accessories — Besides  the  mechanical  plant  so 
far  described,  there  are  a  number  of  minor  structures  which  are 
deserving  of  mention.  These  will  be  briefly  described  without 
particular  regard  to  location  and  importance.  To  supply  pure 
water  to  the  offices,  workmen's  dwellings  and  other  places 
wThere  potable  water  is  required,  there  are  two  filters,  the 
smaller  of  which  is  held  in  reserve  for  emergencies.  The  larger 
or  main  filter  is  built  of  reinforced  cement  and  is  roofed  over. 
It  is  io.8m.  (35.4  feet)  long,  5.3m.  (17.4  feet)  wide,  and  3.6m. 
(n.8  feet)  deep,  with  a  bed  formed  of  gravel  and  superim- 
posed layers  of  clean  washed  sand. 

There  are  bath  houses  for  the  workmen  and  engineers.  That 
for  the  workmen  is  a  building  37m.  (121.4  feet)  long  and  13111. 
(42.6  feet)  wide ;  here  the  men  leave  their  home  attire,  and  can 
also  bathe  before  changing  into  it  from  their  working  clothes. 
The  soiled  working  clothes  are  stored  in  a  special  drying  room 
equipped  with  numerous  cords  carried  over  pulleys ;  these  have 
at  one  end  metal  hooks  and  soap  dish ;  the  soiled  garments  are 
hung  to  these  hooks  and  hauled  up  to  the  ceiling  to  dry.  Each 
workman  has  his  individual  cord.  The  bridge  leading  to  these 
workings  is  roofed  over  and  boarded  in  to  prevent  a  too  brusque 
transition  from  the  heat  of  the  tunnel  to  the  cold  outside  air. 
The  workmen's  bath  rooms,  80  in  number,  are  lighted  by  elec- 
tricity and  kept  at  a  constant  temperature  of  22 °C.  by  steam 
pipes.  The  engineers'  bath-house  has  about  a  dozen  rooms 
with  tub  and  shower  baths. 

Behind  the  baths  are  situated  the  two  hot-water  boilers. 
Here,  too,  are  the  laundries,  fitted  up  with  large  barrel  washing 
machines,  centrifugal  wringers,  etc.  These  handle  only  the 
linen  of  the  engineers  and  higher  employes ;  the  miners  gener- 
ally live  with  their  families  and  have  their  work  done  at  home. 
In  the  power-house  there  is  a  small  Linde  ice-making  plant. 
A  number  of  habitations  for  workmen  have  been  erected  on 
the  works,  but  the  greater  number  of  these  prefer  to  live  in  vil- 


THE  CONSTRUCTION  OF  THE  SIMPLON  TUNNEL  265 

lages  which  have  sprung  up  about  Iselle  and  at  the  bottom  of 
the  Tasquera  cliffs. 

Owing  to  the  rigid  discipline  enforced  and  to  the  natural 
prudence  of  the  Italian  workman,  accidents  are  remarkably 
few.  Full  provision  is,  however,  made  at  both  ends  of  the  tun- 
nel to  care  for  accidents.  At  the  Italian  end  urgent  cases  and 
minor  injuries  are  treated  in  a  free  dispensary  located  just  at 
the  entrance  to  the  tunnel  bridge,  and  where  a  surgeon  and  at- 
tendant are  always  stationed.  The  more  serious  accidents  are 
treated  in  a  hospital  provided  with  40  beds  and  in  charge  of  a 
physician  and  two  assistants.  Here  the  miner  pays  30  cents  a 
day  for  the  care  which  he  receives.  The  miners  are  all  insured 
by  the  company.  The  married  engineers  live  with  their  fami- 
lies. A  large  boarding  house  with  clubrooms  and  reading- 
rooms  is  provided  for  the  unmarried  engineers.  Near  this  club- 
house is  a  large  three-story  building  used  for  the  constructors' 
offices,  and  higher  up  the  valley,  near  the  ventilator  house,  is 
the  two-story  office-building  of  the  Jura-Simplon  Railway. 
Herr  Brandau,  who  directs  the  work  at  the  Italian  end,  has  a 
villa  on  the  hillside  above  Iselle  village.  There  are  also  a 
bonded  storehouse  and  lodgings  for  customs  guards  and  the 
police  provided  by  the  Italian  Government. 

Transportation  Service — The  transportation  service  is  natur- 
ally one  of  the  most  important  services  connected  with  the  tun- 
nel work.  The  motive  power  used  consists  at  both  ends  of 
steam  locomotives,  compressed-air  locomotives  and  horses.  The 
steam  locomotives,  of  which  four  are  employed  at  each  end, 
are  small  six-wheeled  four-coupled  engines,  with  24§-inch 
drivers  and  lox  iif-inch  cylinders,  carrying  about  12  tons  on 
drivers.  The  smokestack  is  hinged,  and  the  engine  has  no 
steam  dome.  The  fuel  burned  is  mixed  coal  and  coke  and  is 
practically  smokeless.  Three  compressed-air  locomotives  are 
also  employed  at  each  end  of  the  tunnel.  These  have  27  tubu- 
lar reservoirs,  with  a  capacity  of  2,000  liters,  carrying  a  pres- 
sure of  70  atmospheres  per  square  centimeter,  which  is  reduced 
to  15  atmospheres  before  entering  the  cylinder.  The  single  cyl- 
inder, 125  x  I5omm.,  is  placed  horizontally  between  the  frames 


266  MODERN    TUNNEL    PRACTICE 

and  drives  the  forward  axle  through  gearing  with  a  reduction 
of  i  to  3.25.  The  driving  wheels  are  62omm.  in  diameter,  and 
the  total  weight  available  for  adhesion  is  6,500  kgs.  To  re- 
plenish the  hot-water  reservoir  there  is  a  steam  boiler  in  the 
tunnel  or  hose  connection  is  made  with  one  of  the  steam  locomo- 
tive boilers.  All  steam  and  air  locomotives  were  furnished  by 
the  Locomotiven  Maschinenfabrik,  of  Winterthur,  Switzer- 
land. 

The  service  railway  has  a  gage  of  8ocm.,  with  rails  weigh- 
ing 15  kgs.  and  20  kgs.  per  meter  laid  on  pressed-steel  ties. 
There  are  three  types  of  spoil  cars :  narrow  ones  of  wood  1.411]. 
(4.6  feet)  wide,  for  the  buildings,  worked  by  horses;  large 
dump  and  flat  cars  for  masonry.  The  dump  and  flat  cars  are 
i. 8m.  (5.9  feet)  wide,  and  the  dump  cars  have  a  capacity  of 
1.6  cu.  m.  These  cars  are  run  in  trains  of  from  4  to  14  cars, 
according  to  the  needs  of  the  work.  They  were  furnished  by 
Arthur  Koppel,  of  Bochteim,  Germany.  The  passenger  cars 
are  mounted  on  spiral  springs  and  carry  24  men  each;  they 
are  run  in  trains  of  18  cars. 

At  the  Italian  end  of  the  tunnel  the  transportation  service  is 
through  Tunnel  i,  since  Tunnel  2  is  occupied  for  the  drainage 
of  the  tunnel.  The  steam  locomotives  work  up  to  4,400111. 
(14,435  ^et)  and  from  this  point  the  air  locomotives  work  to 
within  300m.  or  4Oom.  (984  feet  to  1,317  feet)  of  the  heading. 
This  remaining  distance  to  the  heading  is  served  by  horses,  of 
which  there  are  eight  employed.  At  the  Swiss  end  of  the  tun- 
nel the  haulage  is  by  the  main  tunnel  part  of  the  distance,  and 
then  by  the  side  tunnel,  the  last  few  hundred  feet  being  served 
by  horses.  At  the  Italian  end  there  are  from  26  to  32  trains 
daily  operated  on  a  regular  time  schedule. 

Methods  of  Construction — To  understand  clearly  the  details 
of  the  methods  of  construction,  some  further  account  of  the 
tunnel  structure  is  necessary.  The  structure  extends  from  a 
place  called  Bafn*,  a  few  miles  from  Brieg  on  the  River  Rhone,, 
to  a  point  near  the  village  of  Iselle,  in  Italy.  The  distance  be- 
tween portals  is  19,729111.  (12.4  miles).  The  alignment  is 
straight,  except  for  a  short  curve  at  each  end.  The  curve  at  the 


THE  CONSTRUCTION  OF  THE  SIMPLON  TUNNEL 


267 


Swiss  end  turns  to  the  northwest  and  has  a  radius  of  250111. 
(820  feet),  or  is  a  7°  curve,  and  that  at  the  Italian  end  turns 


Tunnel  No.Z. 


Tunnel  No.  I. 
n.oo1"  —  ' 


For  Heavy  Lateral  Pressure. 

FIG.   123. — Simplon  Tunnel:   Standard  Sections  in  Various  Kinds  of 

Material. 

to  the  east  and  has  a  radius  of  45bm.  (1,476  feet),  or  is  a  3° 
53'  curve.    The  elevation  of  the  Swiss  portal  is  2,250  feet,  and 


268 


MODERN    TUNNEL    PRACTICE 


that  of  the  Italian  portal  is  2,076  feet  above  the  sea.  The  high- 
est point  of  the  tunnel  is  a  level  stretch  of  50001.  (1,640  feet) 
at  an  elevation  of  2,310  feet,  located  about  midway  between 
portals.  From  this  summit  level  the  line  descends  on  a  0.2% 
grade  to  Brieg  and  on  a  0.7%  grade  to  Iselle.  These  are  the 
longitudinal  characteristics  of  the  tunnel. 

Transversally  the  tunnel  consists  of  twin  single-track  tunnels 
exactly  parallel  in  plan  and  profile.  These  parallel  tunnels  are 
spaced  I7m.  (55.76  feet)  apart,  c.  to  c.,  and  are  planned  to  be 
identical  in  sectional  profile.  The  adopted  profiles  for  the  dif- 
ferent materials  are  shown  by  the  drawings  in  Fig.  123.  At  the 
summit  level  the  cross-section  is  increased  in  dimensions  to 
accommodate  two  tracks.  At  present  only  one  of  the  twin 


FIG,  124. — Plan  of  Portion  of  Twin  Tunnels,  Showing  Cross-gallery. 

tunnels  is  being  constructed  to  its  full  dimensions ;  the  other  is 
being  opened  by  a  small  gallery  which  serves  for  drainage,  ven- 
tilation and  other  services  connected  with  the  tunnel  work. 
These  characteristics  are  clearly  indicated  by  the  drawings  of 
Fig.  123.  At  intervals  of  about  2OOm.  (656  feet)  the  service 
gallery  and  the  tunnel  are  connected  by  transverse  galleries, 
as  shown  by  the  partial  plan,  Fig.  124.  The  uniform  distance 
apart  of  these  cross-galleries  has  been  interfered  with  at  a  few 
points  where  special  conditions  demanded  changes  in  the 
adopted  plans,  but  normally  they  were  constructed  as  shown  by 
Fig.  124  and  were  spaced  2Oom.  apart. 


THE  CONSTRUCTION  OF  THE  SIMPLON  TUNNEL 


269 


The  tunnel  is  lined  throughout  with  masonry,  the  cross-sec- 
tion of  the  lining  masonry  varying  with  the  character  of  the 
material  penetrated,  as  shown  by  Fig.  123.  The  normal  sec- 
tion of  the  lining  is  interrupted  at  intervals  by  niches  and  side 
chambers.  These  are  of  three  forms,  as  shown  in  Fig.  125. 
At  every  looth  meter  there  is  a  small  refuge  niche  of  the  con- 
struction shown  by  a;  at  every  kilometer  (0.62  mile)  there  is 
a  small  chamber  constructed  as  shown  at  b,  and  every  four  or 


EMO. 
NEWS. 

Longitudinal  Section.  Eleva-Hon. 

FIG.   125.— Details  :    a  =  small  refuge  niches;  b  =  small  chamber;  c  =  lat- 
eral chamber  and  elevation. 

five  kilometers  there  is  a  large  chamber  constructed  as  shown 
at  c.  It  will  be  observed  that  these  large  chambers  are  designed 
to  penetrate  from  tunnel  to  tunnel,  when  the  second  tunnel  is 
developed  to  its  full  section.  In  conclusion  it  should  perhaps 
be  noted  that  the  tunnel  masonry  terminates  at  each  end  in  a 
portal  of  architectural  design. 

Alignment. — To  describe  in  detail  the  method  of  fixing  the 
center  line  of  the  Simplon  tunnel  would  involve  a  description 
of  special  surveying  operations  which  would  run  into  great 


270 


MODERN    TUNNEL    PRACTICE 


length,  and  we  shall,  therefore,  simply  outline  the  general  plan 
of  operations.  These  comprised  the  usual  location  of  the  sur- 
face axis  and  terminals  and  the  establishing  of  reference  points 
from  which  the  axis  could  be  transferred  underground,  and 
also  the  usual  periodical  surveys  by  which  the  underground 
workings  were  directed.  A  preliminary  surface  survey  of  the 
tunnel  line  was  made  in  1898,  and  in  1899  the  line  was  finally 
and  carefully  located  by  a  system  of  triangulation  connecting 
onto  the  main  Swiss  triangulation  system.  This  survey  gave 
the  engineers  the  necessary  reference  points  at  each  end  of  the 
tunnel  from  which  the  surface  axis  could  be  carried  under- 
ground. The  daily  direction  of  the  work  underground  in- 
volved no  unusual  features.  A  verification  of  the  underground 


Cross    Section.  Longitudinal    Section. 

FIG.  126. — Simplon  Tunnel :  Sequence  of  Excavation. 

line  is  made  each  month,  every  three  months  and  once  a  year, 
using  separate  sets  of  instruments  for  each  of  the  surveys.  The 
quarterly  verifications  are  made  with  particular  care,  and  at 
the  time  of  the  annual  verification,  which  is  made  on  December 
4,  or  the  anniversary  of  Santa  Barbara,  all  work  is  stopped  and 
the  tunnel  is  cleared  and  specially  ventilated  for  the  surveying 
operations.  The  fixed  points  in  the  tunnel  are  located  every 
loom.  (328  feet),  or  2Oom.  (656  feet),  and  are  marked  during 
surveying  operations  by  acetylene  lamps. 

Normal  Methods  of  Excavation — The  methods  adopted  for 
excavating  the  Simplon  tunnel  can  be  divided  into  ( i )  the 
method  normally  followed,  and  (2)  a  modification  of  this 


THE  CONSTRUCTION  OF  THE  SIMPLON  TUNNEL 

method,  which  is  employed  on  certain  difficult  sections  of  the 
work.  It  may  be  premised  further  that  the  specific  methods 
described  are  those  followed  at  the  Italian  end  of  the  work. 
The  work  at  the  Swiss  end  is,  however,  carried  on  in  a  much 
similar  manner. 

Sequence  of  Excavation — The  sequence  of  excavation  fol- 
lowed in,  taking  out  the  tunnel  section  is  shown  diagrammati- 
cally  by  Fig.  126.  The  center  bottom  drift  is  first  driven  by 
means  of  power  drills  and  is  then  timbered  and  covered  with  a 
closely  boarded  roof.  From  this  drift  a  shaft  is  driven  upward 


FIG.    127.— Sections    Showing   Construction   of  Brandt   Rotary   Drift. 

to  the  roof  line  every  5om.  ( 164  feet).  The  top  heading  No.  2 
is  then  excavated  by  working  in  both  directions  from  each  of 
these  shafts.  Next  in  order  is  the  removal  of  the  shallow  trans- 
verse section  No.  3  and  then  the  two  side  cheeks  No.  4.  It  will 
be  observed  that  no  disturbance  of  the  timbered  drift  No.  i 
occurs  during  the  excavation  of  parts  No.  2  and  No.  3,  so  that 
traffic  through  the  drift  goes  on  uninterruptedly. 


272 


MODERN    TUNNEL    PRACTICE 


Power  Drilling  Operations — The  advance  drift  No.  I  is  the 
only  part  of  the  excavation  performed  by  power  drills.  The 
drills  employed  are  Brandt  rotary  drills,  the  construction  and 
mounting  of  which  are  shown  by  Figs.  127  and  128.  The  feed 
of  the  rotary  cutting  tool  is  accomplished  by  the  direct  pressure 
of  water  in  a  large  cylinder,  the  piston  of  which  returns  auto- 
matically when  the  water  supply  is  cut  off.  The  mandril  car- 
rying the  boring  bar  and  also  the  cutter  are  driven  by  means  of 
two  cylinders  located  above  the  feed  cylinder.  These  cylinders 


FIG.  128. — Brandt  Drill,  Mounted  for  Operation. 

operate  a  shaft  having  a  worm  gear  which  meshes  with  a  worm 
wheel  centered  on  the  mandril.  The  cylinders  are  ij-  inches  in 
diameter  and  their  pistons  have  a  stroke  of  2§  inches.  They 
are  operated  by  hydraulic  pressure  and  each  uses  normally  i 
liter  of  water  per  second.  The  two  cylinders  are  connected  by 
cross  waterways  and  the  piston  of  one  acts  as  the  valve  of  the 
other.  The  speed  of  the  cutter  necessarily  varies  for  different 


THE  CONSTRUCTION  OF  THE  SIMPLON  TUNNEL  273 

densities  of  rock,  but  its  highest  speed  is  ten  revolutions  per 
minute.  The  drill  as  described  is  mounted  in  groups  of  two  or 
more  on  a  heavy  iron  thrust-bar  about  12  inches  in  diameter. 
This  thrust-bar  is  pivoted  to  the  drill  carriage  and  is  counter- 
balanced, as  shown  in  Fig.  128.  It  will  be  clear,  of  course, 
that  all  holes  bored  by  the  drill  must  radiate  in  direction  from 
the  transverse  thrust-bar  as  an  axis. 

In  the  Simplon  tunnel  work  the  drills  are  mounted  in  groups 
of  three,  and  one  carriage  is  worked  in  each  heading.  Nor- 
mally there  are  two  headings  in  progress,  namely,  the  advance 
drift  No.  i  in  the  tunnel,  and  the  service  gallery.  At  times  two 
headings  have  been  worked  in  the  tunnel,  making  three  sets 
of  drills  and  nine  boring  heads  in  operation.  The  hollow  head 
or  cutter  is  3  inches  in  outside  diameter  and  has  a  bore  ij 
inches  in  diameter.  The  depth  of  the  hole  bored  is  usually  4-J 
feet,  and  different  lengths  of  boring  bars  are  employed  to  suit 
the  more  or  less  worn-up  condition  of  the  cutter  head.  This 
is  attached  to  the  boring  bar  by  a  one-quarter  turn  of  a  square 
quadruple  threaded  screw.  The  number  of  square  heads  em- 
ployed is  considerable,  there  being  24  allotted  to  the  Italian  end 
of  the  work. 

In  normal  operation  the  work  proceeds  as  follows :  The 
thrust  beam  is  wedged  between  the  two  side  walls  of  the  head- 
ing by  means  of  timber  blocking.  The  holes  are  then  started 
by  means  of  a  V-shaped  center  bit,  each  hole  being  located  with 
due  regard  to  the  rock  seams  and  stratification  and  so  as  to 
obtain  the  best  blasting  effect  possible.  After  the  holes  have 
been  started  the  center  bits  are  replaced  by  the  rotary  cutters. 
The  time  taken  to  bore  one  hole  varies  considerably,  but  it  may 
be  estimated  from  the  daily  advance  made,  which  is  given  below. 
Ordinarily,  ten  or  eleven  holes  are  bored.  The  section  at  the 
heading  is  nominally  6^  x  9^  feet,  or  6i|  square  feet,  and  as  the 
depth  of  each  blast  is  roughly  4^  feet,  the  cubic  contents  re- 
moved with  each  blast  is  from  265  to  275  feet.  During  the  early 
stages  of  the  work,  and  again  recently,  the  number  of  blasts 
amounted  to  only  four  or  five  per  day,  and  the  average  daily 
advance  for  the  month  was  about  16  feet  at  the  Italian  end,  and 


2/4  MODERN    TUNNEL    PRACTICE 

from  20  to  21  feet  at  the  Swiss  end.  This  work  was  in  a 
gneiss  rock.  In  rock  of  a  more  friable  nature,  such  as  the 
anhydrite  or  lime  sulphate,  an  advance  of  as  much  as  34  feet 
has  been  made  in  24  hours.  After  each  blast  the  time  required 
to  clear  the  heading,  set  the  drills,  complete  the  boring  and 
remove  the  drill  carriage  to  a  point  of  safety  is  upward  of  an 
hour. 

The  cutter  is  aided  in  its  work  by  the  water  discharged  into 
its  interior  from  the  cylinders.  This  water  emerges  from  the 
drill  hole  around  the  outside  of  the  cutter  and  carries  with  it 
the  borings  in  the  form  of  a  coarse  powder.  The  cutter  teeth 
are  set  with  a  clearance  of  about  ^-inch,  so  that  the  hole  bored 
is  3^  inches  in  diameter  or  -J-inch  larger  than  the  cutter  cylin- 
der. This  amount  of  clearance  is  ample  to  keep  the  cutter  from 
binding  and  to  permit  the  drill  hole  to  be  readily  freed  from  all 
borings.  When  desired,  the  water  may  be  discharged  direct 
from  the  cylinders  without  entering  the  cutter.  Except  in  the 
very  hardest  rock  no  core  is  formed  by  the  drill. 

Explosives — The  explosives  used  are  dynamite  at  the  Italian 
end  and  blasting  gelatine  at  the  Swiss  end.  The  following  are 
the  compositions  of  these  two  materials : 

Dynamite.  Gelatine. 

Nitroglycerine 83%  64% 

Octomitric  cotton 5%  3% 

Potassium   nitrate 10% 

Cellulose    2%  8% 

Soda  nitrate —  24% 

Carbonate  of  magnesia —  i% 

Total   100%  100% 

At  the  Italian  end  the  dynamite  storage  house  is  located  at 
Varzo,  about  one  and  one-half  miles  from  the  tunnel  portal, 
and  each  day's  supply  is  taken  from  here  and  transported  on  a 
push  car  to  a  storehouse  located  in  one  of  the  cross-galleries  of 
the  workings. 


THE  CONSTRUCTION  OF  THE  SIMPLON  TUNNEL  275 

Mining  Operations — The  dynamite  is  put  up  in  i-kg\  ( I  Ib. ) 
packages,  and  each  hole  is  charged  with  six  packages.  Each 
blast,  therefore,  represents  from  60  to  66  pounds  of  explosive. 
The  charges  are  fired  by  means  of  ordinary  fuses,  which  are 
so  cut  as  to  give  a  half  minute  interval  between  the  firing  of 
successive  holes.  The  blast  frequently  throws  the  fragments  of 
rock  to  some  distance,  and  all  machinery  which  can  be  re- 
moved, as  well  as  the  men,  takes  refuge  in  the  cross-galleries 
and  the  service  gallery  of  Tunnel  No.  2. 

About  10  or  15  minutes  are  required  after  each  blast  to  clear 
the  heading  of  fumes.  This  is  accomplished  by  means  of  the 
ventilating  pipe,  which  runs  close  up  to  the  face,  and  by  means 
of  a  spray  operated  from  the  pressure  pipes.  The  ventilating 
pipe  exhausts  about  35  cubic  feet  of  air  per  second,  and  the 
spray  is  particularly  useful  in  absorbing  the  sulphurous  gases. 

The  spoil  from  the  blast  is  cleared  away  from  the  face  by  one 
gang  of  men,  while  another  loads  the  collected  rock  onto  nar- 
row-gage cars  hauled  by  horses.     No  tools  are  used,  all  the 
material  being  handled  by  manual  labor  alone.    Every  effort  is 
made  to  rush  this  work  of  clearing  the  heading  so  that  the  drills 
may  be  got  back  to  work  as  soon  as  possible.     To  this  end  the 
clearings  gangs  are  composed  of  men  who  have  been  previously 
rested  by  performing  light  work  only,  and  only  the  most  skilled 
and  energetic  laborers  are  employed.     The  majority  of  the 
laborers  are  southern  Italians,  both  at  the  Italian  and  the  Swiss 
ends.     Some  Swiss  and  a  few  Prussians    are   employed,  but 
mostly  in  connection  with  the  machine  work.    There  are  14  or 
15  men  at  each  heading  and  they  are  worked  in  three  shifts 
daily.     Each  gang  has  two  horses  for  each  shift.     These  are 
supplied  by  a  local  peasant  job  master  at  $1.60  per  day,  and 
each  horse  works  eight  hours  a  day,  with  an  occasional  day's 
rest.     The  horses  die  off  quite  rapidly,  and  each  death  is  paid 
for  by  the  tunnel  contractors.    Various  other  methods  of  trans- 
portation have  been  considered  and  a  few  others  have  been  ex- 
perimented with,  but  none  has  appeared  to  the  engineers  to 
offer  any  economy  over  horses  for  transportation  in  the  advance 
heading.     The  horses  take  the  cars  to  compressed-air  locomo- 


276 


MODERN    TUNNEL    PRACTICE 


lives  and  these  in  turn  take  them  to  steam  locomotives,  as  de- 
scribed before. 

Timbering — The  timbering  of  the  tunnel  excavation  com- 
prises, first,  the  timbering  of  the  bottom  advance  drift ;  second, 
the  timbering  of  the  vertical  shafts,  and,  third,  the  timbering  of 
the  top  heading  and  the  enlargements.  All  portions  of  the  work 
are  timbered.  The  timber  ordinarily  and  generally  used  for 
timbering  at  the  Italian  end  is  birch  and  fir  cut  from  the  moun- 
tain slopes  above  Iselle  and  conveyed  to  the  tunnel  entrance 
by  wire  ropeways.  The  amount  of  timber  used  is  large  and  a 
considerable  force  of  lumbermen  is  kept  steadily  at  work  by  the 
contractors. 

The  timbering  of  the  bottom  drift  or  advance  gallery  con- 


FlG.  129.     (i) — Standard  Timbering;   (2) — Extra  Heavy  Timbering. 

sists  of  quadrangular  frames  set  at  intervals  and  .carrying  a 
longitudinal  lagging  on  their  caps.  The  side  posts  are  some- 
times vertical  and  sometimes  have  a  slight  batter,  and  the 
frames  are  with  or  without  sills,  according  to  the  transverse  lay 
of  the  rock  seams.  The  several  drawings,  Figs.  129-130  inclu- 
sive, all  indicate  quite  clearly  the  nature  of  the  advance  gallery 
timbering.  These  drawings  show  various  designs  of  the  full 
section  timbering  used.  The  form  shown  by  Fig.  129  (i)  is 
ihe  one  preferred  when  it  can  be  used,  but  that  shown  by  Fig. 


THE  CONSTRUCTION  OF  THE  SIMPLON  TUNNEL 


277 


129  (2)  is  much  used,  particularly  at  shafts  and  where  shelling 
of  the  roof  rock  layers  is  liable  to  occur.  Fig.  130  shows  the  tem- 
porary fan-shaped  timbering  employed  in  opening  up  the  roof 
gallery.  Ultimately  the  radiating  struts  B,  C  and  D  are  re- 
placed by  the  full  section  members  A',  B',  C'  and  D'  as  the  ex- 
cavation is  developed.  In  the  full  section  timbering  the  trans- 
verse frames  are  spaced  8  feet  and  10  feet  apart  and  sometimes 
even  greater  distances,  depending  upon  the  nature  of  the  rock 
penetrated. 

Lining — The  tunnel  is  lined  with  coursed  masonry  from  end 
to  end,  and  the  character  of  the  masonry  at  different  points  is 


FIG.    130. — Progressive   Stages   in   Arch   Timbering  During  Enlargement. 

shown  by  the  standard  sections  of  Fig.  123.  Fig.  125  shows 
the  masonry  work  of  the  niches  and  side  chambers.  The  facing 
stone  of  all  this  masonry  is  antigorio  gneiss  at  the  Italian  end. 
Under  normal  conditions  the  lining  is  built  as  fast  as  the  en- 
largement of  the  section  is  completed,  but  where  water  has  been 
encountered,  or  where  the  rock  is  of  unstable  character,  there 
has  often  been  a  distance  of  1,300  feet  between  the  completed 
side  walls  and  the  end  of  the  enlarged  section,  and  of  1,600 
feet  between  the  latter  point  and  the  arch  masonry.  The  en- 
deavor of  the  engineers  is  always  to  keep  the  lining  close  up  to 
the  enlargement. 


278 


MODERN    TUNNEL    PRACTICE 


The  method  of  constructing  the  lining  is  to  build  the  side 
walls  up  to  the  springing  lines  and  then  to  follow  with  the  roof 
arch  masonry.  The  walls  being  built,  a  vertical  frame,  com- 
posed of  a  cap,  a  sill  and  posts,  is  set  up  as  close  to  each  as  the 
batter  of  the  walls  will  allow.  These  frames  are  about  lorn. 
(32.8  feet)  long  and  are  indicated  at  A  A  in  Fig.  131.  Trans- 
verse timbers  are  placed  so  as  to  span  across  the  space  between 
these  frames  and  carry  a  flooring.  On  this  flooring  are  set  the 
ribs  for  the  arch  center.  These  ribs  are  composed  of  two  7-inch 
I-beams  bent  edgewise  and  connected  by  bolts  at  the  crown. 


Sectjfn 
° 


FIG.  131. — Diagram  Showing  Method  of  Constructing  Lining. 

They  are  adjusted  to  elevation  by  means  of  wedges  under  their 
ends,  and  carry  a  timber  lagging  on  which  the  arch  masonry 
rests.  As  will  be  seen  from  Fig.  131,  the  staging  is  of  such 
dimensions  that  the  material  cars  pass  freely  underneath  it,  and 
the  arch  material  is  hoisted  from  these  cars  to  the  platform  by 
means  of  a  chain  hoist. 

Where  there  is  a  strong  discharge  of  water  from  the  roof 
rock  it  is  diverted  during  the  construction  of  the  arch  ring  by 
means  of  metal  shields  or  plates  set  below  the  roof  poling- 
boards,  and  when  the  ring  has  been  completed  and  the  brick  fill- 
ing is  being  placed  a  channel  is  formed  in  the  latter  to  take  the 


THE  CONSTRUCTION  OF  THE  SIMPLON  TUNNEL 


279 


water  down  behind  the  arch  ring  and  the  side  wall,  to  the  foot 
of  which  is  a  passage  to  the  main  drain  formed  in  the  floor  of 
the  tunnel  at  one  side.  This  drainway  is  formed  in  hydraulic 
cement,  as  indicated  by  Fig.  131,  which  shows  the  spring  lo- 
cated on  the  haunch  opposite  to  the  tunnel  drain,  thus  requiring 
a  cross-passage  in  the  tunnel  floor.  In  some  instances  where 
there  has  been  a  small  leak  in  the  roof  rock  it  has  been  con- 
nected with  a  J-inch  or  f-inch  pipe  led  down  through  the  fill- 
ing and  arch  ring,  and  then  carried  down  the  soffit  and  side 
'wall. 

The  thickness  of  the  arch  ring  varies  from  14  inches  in  solid 


e...:._f  Z.so'?—- M 

EN&.NEWS 

FIG.  132.— Lining  Used  for  Very  Heavy  Pressures. 

rock  to  20  inches  and  24  inches  in  friable  rock;  in  exceptional 
cases,  such  as  are  noted  further  on,  the  arch  ring  has  been  made 
upward  of  4  feet  thick.  The  filling  above  the  arch  ring  is 
cemented  rubble,  and  it  amounts  to  about  three  cubic  feet  per 
lineal  foot  of  tunnel. 

Materials  Penetrated  at  Italian  End — It  will  be  remembered 
that  the  working  entrances  at  the  Italian  end  are  on  the  line  of 
the  tunnel  tangent  extended.  The  short  curve  which  will  form 
the  actual  tunnel  will  be  excavated  toward  the  conclusion  of  the 
work.  Practically  this  same  method  of  opening  up  the  work  is 
followed  at  the  Swiss  end.  The  materials  penetrated,  begin- 


28O  MODERN    TUNNEL    PRACTICE 

ning  at  the  working  entrances  at  the  Italian  end,  have  been  as 
follows :  At  the  entrance  there  was  a  mere  crust  of  ferrous 
quartz.  This  was  followed  for  a  distance  of  4,350111.  (14,268 
feet)  by  a  very  hard  gneiss  lying  in  horizontal  strata  and 
known  as  antigorio.  This  gneiss  contained  occasional  seams  of 
crystalline  rock,  quartz,  sulphur,  pyrites,  etc.  From  meter 
4350  to  meter  4450  the  material  was  calcareous  rock  and 
green  mottled  cipolin.  Previous  to  the  ending  of  the  gneiss 
rock,  however,  water  was  encountered  as  described  in  the 
earlier  part  of  this  article.  Beyond  the  cipolin  for  about  4om. 
(131.2  feet),  or  from  meter  4450  to  meter  4490,  a  disinte- 
grated slate  clay  was  encountered,  which  proved  to  be  a  most 
treacherous  material  and  which  has  up  to  the  present  time  been 
the  most  difficult  part  of  the  whole  tunnel.  The  method  of 
penetrating  this  disintegrated  rock  is  described  in  a  succeeding 
section.  Succeeding  the  disintegrated  slate  there  was  about 
6om.  (196.8  feet)  of  a  jumbled  mixtureof  mica  schist,  schistic 
gneiss,  cipolin,  quartz  and  white  marble.  From  meter  4550  to 
meter  4850  the  rock  was  anhydrite  or  crystalline  sulphate  of 
lime.  Then  followed  calcareous  rock,  schists,  anhydrite,  grani- 
toid rocks  and  schistic  gneiss,  the  last  being  nearly  as  dense  and 
hard  as  the  antigorio  first  encountered.  All  these  rocks  were 
in  horizontal  strata.  These  conclude  the  list  of  materials  so  far 
penetrated. 

As  already  described,  the  method  of  penetrating  the  mater- 
ials described  was  to  open  an  advance  bottom  'drift  by  means  of 
power  drills,  then  to  project  upwards  shafts  at  intervals  and  to 
extend  a  top  heading  from  each  of  them,  and  finally  to  enlarge 
this  heading  and  open  up  the  full  profile.  This  enlargement 
was  all  accomplished  by  hand  drilling  and  blasting.  Normally 
this  method  of  excavation  has  proved  satisfactory,  but  when 
the  disintegrated  slate  was  struck  it  failed  entirely,  and  another 
and  special  method  had  to  be  devised  for  carrying  on  the  work. 
This  method  will  now  be  described  so  far  as  it  has  been 
developed. 

Methods  of  Excavating  Through  Disintegrated  Rock The  dis- 
integrated slate  clay  was  a  water-soaked  coarse  powder  abso- 


THE  CONSTRUCTION  OF  THE  SIMPLON  TUNNEL 


28l 


lutely  without  stability.  It  was  penetrated  by  first  opening  a 
bottom  drift  and  then  enlarging  this  drift  and  erecting  the  lin- 
ing. This  was  of  unusually  heavy  section,  and  is  shown  by 
Fig.  132.  At  first  it  was  attempted  to  proceed  by  using  the 
ordinary  timbering  methods  with  timbers  of  unusual  strength, 
but  the  crushing  of  this  timber  soon  put  a  stop  to  the  task. 
First  one  thing,  then  another,  was  tried  in  the  way  of  special 


Elevation  . 


Longitudinal  Section.' 


Sectional     Plan 


FIG.  133. — I-beam  and  Timber  Lining. 

timbering,  but  all  of  them  failed,  and  no  success  was  had  until  a 
combination  method  of  steel  and  timber  strutting  was  em- 
ployed. This  is  shown  in  the  succeeding  illustrations,  Figs. 
133  to  136. 

Advance  Drift. — The  advance  drift  was  excavated  by  opening 
first  a  5  x  5^-foot  drift  near  the  bottom  and  timbering  it  with 
rectangular  frames  sheeted  with  poling-boards  on  all  four  sides. 
This  small  drift  was  then  enlarged  by  taking  out  a  heading 
above  it  and  working  down  the  sides.  In  the  enlarged  section 
a  lining  composed  of  special  I-beam  and  timber  frames  was 
then  placed.  Beyond  the  general  statement  given  it  is  not  possi- 


282 


MODERN    TUNNEL    PRACTICE 


ble  to  describe  the  mode  of  operation.  The  excavation  and 
timbering  was  done  piecemeal  by  scraping  away  a  bit  at  a  time 
and  keeping  the  faces  supported  by  lagging  and  struts  placed 
as  demanded  and  as  would  but  serve  the  immediate  purpose. 
The  final  I-beam  and  timber  lining  was  erected  by  first  placing 
the  sill,  then  erecting  the  cap  and  finally  wedging  in  the  wall 


*  Stage.      j      3^  Stage. 

FIG.  134. — Sequence  of  Operations  in  Soft  Rock. 

posts.  The  construction  of  these  lining  frames  is  shown  by 
Fig.  133.  In  the  most  difficult  portions  the  frames  are  set  close 
together,  as  illustrated,  so  as  to  form  a  tight  lining,  but  in  more 
stable  material  they  were  spaced  varying  distances  apart  and 
filled  between  with  concrete.  Each  frame  weighed  2,640 
pounds,  and  altogether  74  were  erected.  This  work  was 
enormously  expensive. 


THE  CONSTRUCTION  OF  THE  SIMPLON  TUNNEL  283 

Enlargement  of  Section — The  method  of  enlarging  the  drift 
which  was  timbered  by  the  I-beam  and  timber  frames  is  illus- 
trated by  Figs.  134  and  135,  inclusive.  Work  is  started  by 
chopping  out  the  timbers  between  a  pair  of  the  steel  wall  beams 
at  a  height  convenient  for  the  passage  of  men  and  materials,  as 
shown  at  B,  Fig.  134.  This  opening  is  framed  with  a  square 
cap  and  sill  and  vertical  side  posts,  leaving  a  clear  opening 
o.Qm.  (2.9  feet)  high  and  of  a  width  equal  to  the  distance  be- 
tween the  iron  frames  less  the  thickness  of  the  side  posts.  EX- 


FIG.   135. — Sequence  of  Operations  in  Soft  Rock. 

cavation  is  begun  horizontally  outward  from  each  opening  until 
a  space  4  feet  deep  and  4  feet  8  inches  high  has  been  excavated 
and  timbered,  and  sheeted,  as  shown  by  Fig.  134,  B,  "first 
stage."  The  timbers  used  are  round  in  cross-section  and  of  the 
dimensions  shown  by  the  drawings  in  centimeters.  This  open- 
ing is  simultaneously  carried  downward,  as  shown  by  the  sev- 
eral stages  of  Fig.  134,  B  and  C,  and  laterally  until  it  has  a 
width  of  about  9  feet  10  inches,  as  shown  by  the  plan,  Fig.  134, 


284 


MODERN    TUNNEL    PRACTICE 


A.  The  work  is  now  ready  for  underpinning  the  steel  frame. 
The  first  operation  is  the  insertion  of  a  longitudinal  8  x  1 2-inch 
timber  under  the  corners  of  the  frames,  as  shown  in  Fig.  134, 

B,  "second  stage."    Under  this  beam  four  1 2-inch  wood  posts 
are  inserted  in  local  cavities  excavated  for  them,  as  shown  by 
Fig.  134,  C,  "fourth  stage."    These  posts  stand  on  a  floor  plate, 
as  shown  in.  Fig.  134,  D,  "fifth  stage,"  and  the  whole  frame  is 
braced  laterally  against  the  wall  and  floor  timbers,  as  shown. 


FIG.  136. — Suggested  Method  for  Building  Roof  Arch  Through  Soft  Rock. 

The  next  operation  is  to  place  a  second  frame  of  cap,  posts  and 
floor  plate  further  under  the  frames.  These  operations  proceed 
simultaneously  from  both  sides  until  the  underpinning  is  com- 
pleted, as  shown  by  Fig.  134,  D  and  E. 

The  next  step  is  to  build  the  center  portion  of  the  masonry 
floor,  as  shown  at  Fig.  135,  F.  Lateral  extensions  of  the  exca- 
vation for  the  side  walls  are  then  made  and  timbered,  as  shown 
by  Fig.  135,  G.  Side  wall  construction  is  then  begun  and  car- 
ried upward,  as  shown  by  Fig.  135,  H  and  7,  until  the  springing 


THE  CONSTRUCTION  OF  THE  SIMPLON  TUNNEL  285 

line  of  the  arch  is  reached.  The  work  described  is  conducted 
from  a  number  of  openings  at  once,  and  these  are  then,  con- 
nected by  breaking  down  the  ends  of  the  section  in  both  direc- 
tions until  the  excavations  and  masonry  meet.  The  method  of 
enlargement  for  the  construction,  of  the  roof  arch  has  not  been 
finally  worked  out,  but  a  plan  which  has  met  with  favor  is  to  fill 
in  the  space  i,  Fig.  136,  with  temporary  masonry  and  then  con- 
struct the  temporary  masonry  arch  2  as  a  center  upon  which 
to  construct  the  permanent  arch. 

Waterworks  Tunnel  at  Cincinnati,  0 — The  new  water  sup- 
ply system  at  Cincinnati,  O.,  includes  an,  intake  tunnel  with 
shaft  and  crib  in  the  Ohio  River,  and  a  tunnel  four  and  one- 
quarter  miles  long  from  the  intake  pumping  station  and  purifi- 
cation plant  to  the  city.  The  system  is  designed  to  supply 
60,000,000  gallons  per  day  (for  a  present  population  of  about 
350,000),  with  provision  for  an  increase  to  90,000,000  gallons 
daily  capacity. 

The  intake  tunnel  under  the  river  is  7  feet  diameter  and 
1,426  feet  long,  with  a  7- foot  intake  shaft  close  to  the  Ken- 
tucky shore,  and  an  8-foot  shaft  at  the  pumping  station  on  the 
Ohio  shore.  The  tunnel  is  lined  with  brick  and  has  a  grade  of 
3  inches  in  100  feet  from  the  intake  shaft  down  to  the  shore 
shaft.  The  shore  shaft  opens  into  a  pump  pit  98  feet  inside 
diameter  and  85  feet  deep.  The  bottom  of  the  pit  is  formed  by 
a  great  timber  caisson  which  was  sunk  into  a  firm  bed  of  sand 
to  within  about  17  feet  of  bed  rock,  and  in  view  of  the  subse- 
quent troubles  it  seems  strange  that  it  was  not  carried  down,  to 
the  rock.  Early  in  1901,  two  cracks  appeared  in  the  shaft 
masonry,  below  the  caisson,  showing  that  under  the  head  due 
to  high  water  in  the  river  the  water  in  the  sand  had  forced  the 
floor  upwards,  the  maximum  movement  being  about  5  inches. 
Investigations  showed  that  the  deck  bulged  up  in  the  middle, 
there  being  no  movement  at  the  sides ;  they  further  showed  that 
the  movements  were  repeated  with  other  stages  of  high  water. 
A  counterbalance  weight  was  built  on  the  center  of  the  deck  and 
this  settled  the  floor  back  2.\  inches,  but  did  not  stop  the  move- 
ments. The  driving  of  tunnels  under  the  caisson  and  building 


286 


MODERN    TUNNEL    PRACTICE 


a  concrete  foundation  so  as  to  form  a  solid  connection  between 
the  caisson  and  bed  rock  has  been  proposed,  but  is  not  now  con- 
sidered necessary.  The  cracks  were  at  first  filled  up — but  after- 
wards this  filling  was  cut  out — all  the  pumping-engine  castings 
available  were  placed  on  the  floor,  and  the  pump  pit  was  filled 
with  water.  At  the  present  time  the  caisson  has  been  forced 
back  to  within  i-iooo  foot  of  its  original  level,  and  it  is  not 
anticipated  that  any  further  trouble  will  be  caused,  especially 
in  view  of  the  great  weight  of  the  pumping  engines  when 
completed. 

Land  Tunnel — The  tunnel  carrying  the  treated  water  to  the 
city  is  22,264  feet  long  from  the  shaft  at  the  clear-water  reser- 


~sw  > 

Alternate  Plan  for 
Connection  of  Hoops 

Elevation. 
Section    under    Little   Miami    River .  Detail  of  End*  of  Hoop*. 

FIG.    137.— Water-works   Tunnel:    Section   of  Land-tunnel. 

voir  to  that  at  the  city  pumping  station.  It  is  approximately 
parallel  with  the  Ohio  River  shore  line  (but  from  300  to  900 
feet  distant)  and  has  a  down  grade  of  i  in  2,000  towards  the 
city.  Its  top  is  60  feet  below  low-water  level,  or  130  feet  below 
high- water  level  in  the  river,  but  when  in  use  the  inside  pressure 
will  be  equivalent  to  90  feet  head.  The  tunnel,  Fig.  137,  is  7 
feet  inside  diameter,  and  lined  with  two  rings  of  specially  made 
radial  pressed  vitrified  shale  brick,  laid  with  close  joints;  the 
inner  surface  is  as  smooth  as  the  best  pressed-brick  building 
work.  The  bricks  are  3  x  4  inches,  9  inches  long,  with  bonding 
grooves  on  the  sides,  and  the  face  curved  to  a  diameter  of  7 
feet.  The  brick  lining  is  backed  with  concrete,  the  minimum 


THE  CONSTRUCTION  OF  THE  SIMPLON  TUNNEL  287 

thickness  of  concrete  being  6  inches.  Where  the  tunnel  crosses 
beneath  the  Little  Miami  River,  the  lining  is  reinforced  by 
rings  of  f-inch  round  steel  bars,  2  feet  c.  to  c.,  as  also  shown  in 
Fig.  137.  The  tunnel  is  completed,  and  in  order  to  determine 
the  amount  of  leakage,  if  any,  it  has  been  filled  with  water  from 
the  city  mains.  The  tunnel  was  driven  through  limestone  and 
shale  rock,  with  about  25  feet  of  rock  above  the  crown.  This 
rock  was  in  some  places  badly  shattered  and  much  water  was 
encountered.  The  pneumatic  or  air-lock  system  was  tried  for  a 
short  distance  (350  feet),  but  did  not  prove  satisfactory.  The 
successful  method  of  dealing  with  the  water  consisted  in  driv- 
ing pipes  into  the  seams,  so  as  to  discharge  the  water  within  the 
tunnel ;  where  the  streams  were  too  small  and  too  numerous  for 
this,  aprons  were  put  in  to  collect  the  water  outside  of  the  lin- 
ing, the  apron  leading  to  a  single  pipe  passing  through  the  lin- 
ing. In  this  way  the  brick  lining  and  concrete  backing  were 
put  in  without  trouble  from  washing,  and  the  pipes  were  left 
projecting  into  the  tunnel.  After  the  work  had  set,  the  pipes 
were  fitted  with  valves,  and  then  cement  grout  was  forced  into 
them  under  80  pounds'  pressure ;  when  no  more  grouting  could 
be  pumped  in,  the  valve  was  closed  and  the  grouting  machine 
transferred  to  another  pipe.  The  grouting  was  found  to  travel 
considerable  distances,  sometimes  appearing  at  other  pipes  be- 
yond where  the  grout  was  being  forced  in.  The  sealed  pipes 
were  left  for  10  or  20  days,  to  insure  thorough  setting  of  the 
grout,  and  they  were  then  cut  off  a  little  back  of  the  tunnel  face, 
and  the  recess  pointed  up.  In  one  place  there  were  300  pipes 
i  to  2  inches  diameter  in  1,000  feet  of  tunnel.  In  spite  of  the 
seamy  rock,  with  direct  connection  to  the  river,  and  in  spite  of 
the  amount  of  water  encountered,  the  finished  tunnel  is  very 
dry,  the  measured  infiltration  being  only  10  gallons  per  minute 
for  the  entire  length. 

Pockets  of  gas  were  encountered  at  several  places,  and  sev- 
eral small  explosions  occurred ;  six  men  were  killed  by  gas  ex- 
plosions. Further  trouble  was  prevented  by  providing  an  in- 
crease of  ventilation  from  the  compressed-air  mains  which  were 
supplying  power  for  the  rock  drills.  The  gas  was  natural  gas, 


288  MODERN    TUNNEL    PRACTICE 

and  this  with  a  little  dilution  with  air  is  less  explosive  than 
marsh  gas  with  much  dilution. 

The  work  was  prosecuted  by  ten  headings  from  the  two  per- 
manent shafts  and  four  intermediate  shafts,  the  latter  being 
afterwards  sealed  and  filled  and  the  tunnel  lining  carried  past 
them.  As  the  center  line  of  the  tunnel  makes  one  or  more 
angles  between  each  pair  of  shafts,  the  survey  work  was  some- 
what complicated,  more  especially  as  buildings  and  other  obsta- 
cles prevented  direct  sights  on  some  of  the  tangents.  The  tan- 
gents were  measured  several  times  at  different  temperatures 
and  the  average  distances  taken.  The  angles  were  also  repeated 
and  averaged,  each  angle  being  measured  no  less  than  ten  times 
and  by  at  least  three  observers.  For  the  levels,  bench  marks 
were  established  at  one-half-mile  intervals.  The  line  was  trans- 
ferred down  the  shafts  by  two  wires,  kept  taut  by  2O-pound 
weights  in  glass  jars  filled  with  glycerine.  The  wires  being 
adjusted  to  line  by  the  transit  over  the  shaft,  were  then  used  by 
the  tunnel  transit  to  project  the  line  upon  scales  set  300  feet 
apart  and  attached  to  anchors  in  the  tunnel  lining.  The  levels 
were  transferred  down  the  shafts  by  measurements  with  steel 
tapes,  the  measurements  being  repeated  and  averaged. 

The  east  end  shaft  is  shown  in  Fig.  138,  but  in  construction 
the  intersection  with  the  opening  for  the  /-foot  nozzle  was  fin- 
ished in  concrete  instead  of  with  a  ring  of  special  brick  as  orig- 
inally designed.  The  interior  lining,  also,  instead  of  being 
brick  on  edge,  as  shown  by  the  drawing,  was  of  special  radial 
or  voussoir-shaped  brick  laid  flat.  Each  brick  used  is  3  x  4 
inches,  9  inches  long,  with  bonding  grooves  top  and  bottom, 
and  a  face  radius  of  5  feet.  The  shaft  is  10  feet  inside  diam- 
eter, and  the  upper  part  is  built  within  a  shell  of  f-inch  steel 
plate,  12  feet  diameter,  extending  to  the  rock  and  having  a 
water-tight  seal.  The  rings  are  6  feet  high,  with  three  plates 
to  a  ring  and  1 6-inch  triple-riveted  vertical  cover  plates.  In 
the  lower  part  the  rings  are  butt-joinied,  with  inside  6-inch 
single-riveted  cover  plates;  but  at  the  top  the  rings  are  lap- 
jointed  and  set  alternately  inside  and  outside.  The  contractors 
for  the  tunnel  were  W.  J.  Gawne  &  Co. 


THE  CONSTRUCTION  OF  THE  SIMPLON  TUNNEL 


289 


Survey  Work  for  the  Land  Tunnel — The  surveying  methods 
employed  for  the  four  and  one-quarter  mile  land  tunnel  to  the 
city  have  been  described  as  follows  in  a  paper  by  Mr.  John  A. 
Hiller,  Assoc.  M.  Am.  Soc.  C.E.,  who  was  Resident  Engineer 
during  construction : 


.    __  Center  of  Tunnel       , 


FIG.    138.— Water- works  Tunnel,   Cincinnati,   Ohio:   East  End   Shaft. 


290  MODERN    TUNNEL    PRACTICE 

"The  construction  was  executed  from  the  permanent  shaft 
at  each  end  and  four  working  shafts,  making  ten  headings. 
The  alignment  of  the  tunnel  not  being  a  continuous  tangent  be- 
tween the  shafts,  but  being  broken  by  one  or  two  angles  be- 
tween, it  became  necessary  to  make  a  very  careful  survey  of  the 
surface  line  to  establish  the  true  position  and  magnitude  of  the 
angles 

"The  centers  of  the  shafts  and  the  angle  points  were  estab- 
lished from  the  preliminary  survey  line,  then  the  tangents  and 
angles  were  measured. 

"Between  shafts  i  and  2  the  line  traverses  a  comparatively 
thickly  built  up  portion  of  the  city.  Tangent  I  passes  through 
a  frame  dwelling;  and  to  obtain  the  line  between  shaft  i  and 
angle  i,  the  transit  was  set  up  on  a  chimney  of  this  house, 
shifted  into  the  line,  and  from  this  position  permanent  points 
were  fixed  on  both  sides  and  foresights  established. 

"Tangent  2  passes  through  the  machine  shop  and  retort 
house  of  the  East  End  Gas  Works,  and  the  office,  stable  and 
coke  piles  of  the  Marmet  Coal  Company.  With  these  obsta- 
cles on  the  line,  it  was  found  impossible  to  get  the  instrument 
at  any  point  where  the  two  extremities  of  the  tangent  could  be 
seen.  A  transverse  line  was  run,  beginning  at  angle  i,  running 
to  angle  2  and  returning  by  another  route  to  angle  i.  This 
was  a  closed  survey,  which  was  divided  by  tangent  2  into  two 
parts,  which,  when  considered  separately,  gave  tangent  2  as  the 
closing  line  for  each  part. 

"The  results  obtained  from  three  trials  of  this  traverse  are 
given  in  Table  i,  each  result  being  the  mean  found  by  consider- 
ing each  part : 

TABLE  i.— MEASUREMENTS  OF  TANGENT  2 
No.  of  trial.  Length  of  tangent  2.    Size  of  angle  i.          Size  of  angle  2. 

ist  1314.5920      15°  27'  32.1"      9°  08'  45.9" 

2d  1314-5892      15°  27'  11.4"      9°  08'  43.1" 

3d  1314-5871       15°  27'  14.6"      9°  08'  49.9" 

Mean  1314.5895       15°  27'  194"      9°  08'  46.3" 

"On  the  third  tangent  there  was  one  building  and  a  pile  in  a 
tramway ;  a  perpendicular  offset  line  passed  these  obstructions. 


THE  CONSTRUCTION  OF  THE  SIMPLON  TUNNEL  2QI 

"The  remainder  of  the  tangents  offered  no  obstacles  which 
could  not  be  overcome  by  the  erection  of  foresights  from  10  to 
20  feet  in  height. 

"The  crossing  of  the  Little  Miami  River  was  made  by  trian- 
gulation,  using  a  quadrilateral,  one  of  whose  diagonals  was  the 
tunnel  line. 

"The  measurement  of  all  tangents  was  made  with  a  5o-foot 
steel  tape,  which  was  ascertained  to  be  correct  at  60°  Fahr., 
with  a  pull  of  14  pounds.  Stakes  were  driven  along  the  line 
every  50  feet ;  and  at  breaks  in  the  ground,  the  line  was  marked 
thereon,  levels  run  to  establish  the  differences  of  elevation  of 
the  stakes,  the  tape  stretched,  and  the  length  and  the  tempera- 
ture of  the  air  for  each  length  was  taken  and  recorded. 

"Each  tangent  was  measured  forward  and  checked  backward 
during  the  summer,  and  the  whole  operation  repeated  later  dur- 
ing the  winter.  In  case  of  any  great  difference  a  check  meas- 
urement was  made.  Thus  each  line  was  measured  at  least  four 
times  uncler  widely  different  weather  and  temperature  condi- 
tions, with  no  accepted  difference  greater  than  one  in  about 
30,000.  A  mean  of  all  measurements  was  taken  as  the  length 
of  the  tangents.  These  mean  measurements  did  not  differ 
more  than  one  in  about  50,000  from  any  extreme. 

"The  field  data  were  tabulated  for  reduction  to  the  horizontal 
distance  and  to  a  temperature  of  60°  Fahr. 

"The  angles  were  measured  by  repeating  each  ten  times,  by 
three  or  more  observers,  and  the  average  result  of  all  observa- 
tions was  accepted  as  the  most  probable. 

"The  bench  levels  were  run  from  an  established  bench  at  Cal- 
ifornia to  near  shaft  i  and  return.  Benches  were  established 
about  every  half  mile,  and  in  the  immediate  vicinity  of  the 
shafts.  Such  parts  of  the  line  where  the  differences  of  the 
two  runs  were  greatest,  a  check  run  was  made  and  the  mean 
differences  of  elevations  used  to  determine  the  elevations  of  the 
benches. 

"Transfer  of  the  Alignment  into  the  Tunnel. — At  each  shaft  an 
observation  station  was  erected  for  each  tangent  and  foresights 
built  at  or  near  the  distant  angle  points.  These  stations  were 


MODERN    TUNNEL    PRACTICE 

so  built  that  the  observer's  platform  was  independent  of  the 
transit  support,  and  all  enclosed  in  a  small  house  to  protect  the 
instrument  from  sun  and  wind.  The  wires  used  for  plumbing 
down  the  shafts  were  No.  5  piano  wire,  about  one-sixtieth  of  an 
inch  in  diameter,  held  in  a  clamp  at  the  top  of  the  shaft  in  such 
a  manner  that  the  wire  could  be  moved  tranversely  by  a  slow- 
motion  screw.  The  method  of  securing  the  device  to  top  of 
the  shaft  cannot  well  be  shown,  as  the  local  conditions  at 
each  shaft  required  a  different  arrangement.  At  the  lower  end 
of  the  wire  was  a  hook,  upon  which  was  hung  a  cylindrical  lead 
weight  of  20  pounds.  The  weights  were  suspended  in  glass  jars 
containing  glycerine.  This  arrangement  permitted  the  weights 
being  seen  at  all  times  and  afforded  absolute  assurance  that  the 
weights  hung  free.  Back  of  each  wire  was  a  small  shield  or 
background  painted  white;  the  lower  end  of  the  wires  being 
blackened,  showed  distinctly  against  the  white  ground.  The 
jar  nearer  the  tunnel  transit  was  supported  on  a  small  stand 
about  3  feet  from  the  floor ;  the  farther  jar  rested  directly  upon 
the  floor  of  the  tunnel.  This  permitted  each  wire  being  viewed 
separately  and  allowed  no  chance  or  confusion  of  viewing  the 
wrong  wire.  An  electric  light  was  supported  so  as  to  throw 
light  upon  the  wire  and  background. 

"The  tunnel  transit  was  supported  on  a  wooden  strut  secured 
against  the  tunnel  arching  by  four  large  set-screws.  A  tripod 
could  not  be  used  on  account  of  the  wooden  floor  being  too 
springy  for  a  secure  set-up. 

"The  tunnel  transit  was  provided  with  a  slow-motion  ar- 
rangement whereby  the  whole  transit  could  be  moved  a  small 
distance  at  right  angles  to  the  tunnel  line,  allowing  of  very 
small  changes  in  the  position  of  the  instrument. 

"The  cross-hairs  of  the  transit  consisted  of  a  diagonal  cross 
and  two  vertical  hairs,  so  spaced  that  they  covered  about  one- 
sixteenth  of  an  inch  at  a  distance  of  about  60  feet.  This  made 
the  sighting  of  the  instrument  very  exact,  as  the  cross-hairs  and 
the  plumb  wire  appeared  white  between,  about  equal  to  the 
diameter  of  the  wire. 


THE  CONSTRUCTION  OF  THE  SIMPLON  TUNNEL  2Q3 


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"The  operation  of  transferring  the  line  into  the  tunnel  con- 
sisted of  setting  a  transit,  in  the  observation  station,  on  line  by 
double  foresights  and  bringing  both  wires  to  this  line  by  means 
of  the  slow-motion  clamps.  The  tunnel  transit  was  then  brought 
into  the  line  of  the  two  wires  and  the  line  transferred  to  the 
scales,  fastened  to  anchors  in  the  masonry  lining  of  the  tunnel. 


294  MODERN    TUNNEL    PRACTICE 

The  scales  were  placed  about  300  feet  apart  and  read  by  ver- 
niers to  o.oi  inch. 

"All  necessary  reversions  of  the  transit  were  made  to  elimi- 
nate all  probable  errors  of  instrumental  adjustment.  Readings 
were  made  on  the  two  scales  and  recorded  for  each  position  of 
the  transit.  Several  independent  trials  were  made,  and  in  all 
about  50  readings  were  taken  on  each  side,  in  each  heading, 
and  a  mean  accepted  as  the  working  base  line  inside  the  tunnel. 
This  line  was  extended  into  the  tunnel  as  the  excavations  were 
advanced,  always  making  the  necessary  reversions  of  the  in- 
strument and  accepting  the  mean  of  all  trials  as  the  correct  line. 

"The  required  distances  from  the  shafts  to  the  angle  points 
were  measured  along  the  roof,  using  the  same  precautions  as  in 
the  measurement  of  the  surface  line.  The  angles  were  turned 
by  repeating  several  times.  Afterward  curves  of  3O-foot  radius 
were  used  for  easing  off  the  intersections.  The  angles  being 
generally  small,  none  of  these  curves  was  long,  and  little  or  no 
additional  excavation  was  needed  in  order  to  place  the  lining  on 
the  curved  line. 

"The  levels  were  transferred  into  the  tunnel  by  steel-tape 
measurements  down  the  shafts.  Four  to  eight  trials  were  made 
at  each  shaft  and  a  mean  result  accepted. 

"Table  2  shows  the  distances  between  the  wires  at  each  shaft, 
the  lengths  driven  in  each  heading,  and  the  errors  for  closing 
for  each  meeting  point. 

"The  engineering  department  took  samples  of  air  from  each 
heading  daily  and  made  tests  for  explosive  gas.  The  daily 
progress  of  each  kind  of  work  in  each  heading  was  measured 
and  recorded  on  a  progress  diagram.  Samples  were  taken  from 
each  shipment  of  cement  and  tests  made  for  soundness  and 
tensile  strength. 

"Lines  and  levels  were  given  in  each  heading  for  every  ad- 
vance of  about  100  feet.  Holes  were  drilled  in  the  roof  about 
every  30  feet  and  plugs  driven,  containing  a  small  staple  in  the 
true  line.  The  distances  from  the  plug  to  the  axis  of  the  tunnel 
were  computed  and  a  list  given  to  the  heading  foreman  for  his 
guidance  in  pointing  the  holes  when  drilling.  These  same 


THE  CONSTRUCTION  OF  THE  SIMPLON  TUNNEL  295 

grades  were  afterwards  used  when  setting  invert  forms.  The 
spring-line  grades  were  marked  on  the  invert  for  setting  the 
arch  centers." 

Telephone  and  Freight  Transportation  Tunnels  at  Chicago. — A 
peculiar  system  of  tunnels  exists  at  Chicago,  consisting  of  a 
network  of  small  tunnels  under  the  streets  (and  including 
nearly  all  the  principal  streets  in  the  downtown  districts). 
These  tunnels  carry  telephone  and  telegraph  cables,  but  are  also 
to  be  operated  for  the  transportation  of  mails  and  freight,  con- 
necting the  several  postoffices,  warehouses,  wholesale  stores,  etc. 
The  tunnels  were  commenced  in  September,  1901,  and  were 
originally  intended  to  carry  the  cables  for  the  automatic  tele- 
phone system  of  the  Illinois  Telephone  Company,  as  it  was 
found  that  the  streets  were  so  completely  occupied  by  water  and 
gas  mains,  sewers,  electrical  conduits,  and  the  various  man- 
holes, that  there  was  no  room  to  be  found  for  conduits  to  ac- 
commodate cables  for  the  proposed  central  exchange  for  100.- 
ooo  subscribers.  It  was  finally  determined,  therefore,  to  build 
a  system  of  tunnels,  and  to  build  these  deep  enough  to  be  within 
the  solid  clay,  and  avoid  disturbance  of  foundations.  The  city 
also  required  them  to  be  deep  enough  to  allow  of  the  future  con- 
struction of  a  subway  system  for  street  cars,  and  the  level  of 
the  tunnel  floor  is  about  30  feet  below  the  street  level.  After  a 
considerable  amount  of  work  had  been  done  the  company  ob- 
tained permission  from  the  city  to  utilize  the  tunnels  for  the 
transportation  of  mails,  express  matter  and  freight,  etc.,  but 
their  use  for  passenger  traffic  is  specifically  forbidden.  In  June, 
1905,  there  were  about  30  miles  completed,  and  the  entire  sys- 
tem will  aggregate  about  60  or  70  miles. 

The  tunnels  are  of  horseshoe  section,  with  a  clear  height  of 
7  feet  6  inches,  and  a  width  of  6  feet ;  they  are  lined  with  con- 
crete, having  a  thickness  of  10  inches  in  the  sides  and  crown 
and  13  inches  in  the  floor.  They  are  driven  in  stiff  blue  clay, 
containing  very  little  water,  but  occasional  pockets  of  gas  and 
of  quicksand  were  encountered.  As  a  precaution  the  work  was 
all  done  on  the  pneumatic  system,  the  air  pressure  being  about 
9  pounds  per  square  inch.  The  air  locks  were  placed  near  the 


296  MODERN    TUNNEL    PRACTICE 

bottoms  of  the  several  shafts ;  they  were  23  feet  long,  and  had 
doors  24  x  36  inches.  No  tunneling  shields  were  used.  The 
material  was  excavated  with  spades  and  draw-knives,  and 
hauled  away  in  small  cars,  20  x  48  inches  inside  measurement, 
to  the  shafts.  These  small  cars  were  used  to  facilitate  handling, 
and  to  enable  a  double  track  of  narrow  gage  (14  inches)  to 
be  laid.  The  shafts  were  sunk  mainly  in  the  basements  of 
buildings,  which  were  utilized  also  for  the  making  of  concrete 
and  storing  of  cars.  In  some  cases,  however,  the  shafts  were 
located  in  the  streets  (at  the  curb  line)  and  were  covered  with 
tall  head-houses. 

The  method  of  construction  was  as  follows  :  The  excavation 
was  made  in  the  clay  for  a  distance  of  about  20  feet,  and  about 
a  foot  larger  than  the  completed  tunnel.  The  1 3-inch  concrete 
bottom  was  then  put  in  place,  and  upon  this  were  placed  forms 
made  of  5-inch  steel  channels  in  two  sections,  curved  to  the 
contour  of  the  inside  of  the  tunnel,  and  put  together  with 
flanged  and  bolted  joints  at  top  and  bottom.  These  ribs  or 
forms  were  3  feet  apart,  and  outside  of  them  were  laid  2-inch 
planks  to  form  the  lagging.  These  planks  were  at  first  20  feet 
long,  but  afterwards  15  feet  was  found  more  satisfactory.  They 
were  laid  one  at  a  time  on  each  side  and  the  concrete  rammed 
into  the  space  between  them  and  the  clay.  When  the  crown, 
forming  the  key,  was  reached,  boards  3  feet  long  were  used. 
The  concrete  was  composed  of  i  part  Portland  cement,  3  parts 
sand  and  5  parts  gravel;  it  was  mixed  by  machines  installed 
in  basements  at  the  heads  of  the  shafts,  and  carried  to  the  work 
in  the  small  cars  on  a  double  track  of  1 4-inch  gage.  The  con- 
crete was  well  tamped  so  as  to  fill  all  voids  and  prevent  any 
subsequent  movement  in  the  mass  of  clay. 

The  work  was  carried  on  continuously  in  three  8-hour  shifts. 
The  mining  gang  (about  7  men)  worked  from  4  p.  m.  to  mid- 
night; this  was  followed  by.  the  trimming  gang  (also  about  7 
men),  which  worked  until  8  a.  m.  in  trimming  the  excavation 
to  proper  form  and  dimensions  and  putting  up  the  centers  and 
lagging.  The  concreting  gang  then  commenced  its  work, 
arranging  it  so  as  to  complete  it  in  time  to  make  way  for  the 


THE  CONSTRUCTION   OF  THE  SIMPLON  TUNNEL 

mining  gang  at  4  p.  m.  Work  was  carried  on  at  about  14 
headings,  with  20  men  to  each.  The  first  12  miles  were  built 
in  lo-J  months,  with  an  average  advance  of  20  to  76  feet  per 
working  day  at  the  different  headings.  In  April  and  May, 
1905,  the  progress  made  was  10,105  feet  (25  working  days) 
and  12,619  feet  (27  working  days)  respectively;  or  an  average 
of  404  to  467  feet  per  working  day.  This  required  the  excava- 
tion of  about  60,000  cubic  yards  of  material. 

The  excavated  material  was  at  first  carried  up  the  shafts  and 
dumped  into  wagons,  this  work  being  done  only  at  night.  When 
one  of  the  tunnels  approached  the  east  side  of  the  river  an  in- 
cline was  built,  up  which  the  cars  were  taken  by  traveling 
chains  having  arms  to  engage  the  axles,  and  the  cars  were 
dumped  into  scows.  Another  incline  was  built  on  the  lake 
front,  where  cars  were  taken  out  by  electric  locomotives  and 
dumped  to  fill  in  the  site  for  Grant  Park.  After  this  latter 
method  of  disposal  had  been  put  into  service,  nearly  all  the 
tunnel  material  was  hauled  out  at  the  lake  front,  as  well  as 
wreckage  from  old  buildings  and  the  material  excavated  for 
deep  foundations  and  basements  of  new  buildings. 

The  tunnel  intersections  above  mentioned  are  very  peculiar. 
The  two  lines  intersecting  at  right  angles  and  on  the  same  level 
are  in  most  cases  connected  by  four  curves  of  2O-foot  radius, 
leaving  four  "pillars"  of  the  original  ground.  Here  the  roof 
is  reinforced  by  steel  I-beams.  The  sharpest  curves  in  the  main 
tunnels  are  of  1 6- foot  radius.  The  lines  are  mainly  level,  with 
maximum  grades  of  1.75%,  and  inclines  not  exceeding  12%, 
Branches  or  spurs  are  run  to  the  postoffices,  stations,  etc.,  to  be 
served,  and  either  enter  a  deep  sub-basement  or  have  a  shaft 
and  elevator  to  the  buildings  with  shallow  foundations. 

The  completed  tunnels  have  a  single  track  of  24-inch  gage, 
laid  with  56-pound  rails  on  cast-iron  chairs  imbedded  in  the 
concrete  floor.  Both  the  overhead  trolley  wire  and  central 
third-rail  conductor  system  of  electric  traction  have  been  tried. 
In  the  latter  case,  the  Morgan  system  is  used,  in  which  the  con- 
ductor is  a  slotted  bar  protected  by  side  timbers  and  gearing 
with  a  contact  or  spur  wheel  on  the  locomotive.  The  tunnels 


298  MODERN    TUNNEL    PRACTICE 

are  well  drained,  lighted  by  electricity,  and  provided  with  tele- 
phones at  frequent  intervals. 

It  is  expected  that  this  system  of  transporting  mails,  newspa- 
pers, parcels,  coal,  freight,  etc.,  as  well  as  wreckage  from  dis- 
mantled buildings  and  material  for  new  buildings,  will  not  only 
facilitate  traffic,  but  also  relieve  the  congestion  of  traffic  in  the 
busy  streets  and  avoid  much  of  the  dirt  and  nuisance  incident 
to  the  hauling  of  refuse  and  building  material  through  the 
streets. 

Tunneling  through  soft  material  in  the  heart  of  a  city  where 
numerous  tall  and  heavy  buildings  exist,  and  where  many  of 
these  buildings  have  foundations  practically  on  the  surface  of 
this  material,  is  a  delicate  kind  of  work  which  was  successfully 
prosecuted  in  these  Chicago  tunnels  for  about  five  years,  with 
practically  no  trouble  from  settlement  of  the  ground.  A  change 
from  the  original  plans,  by  which  the  tunnels  began  to  be  car- 
ried under  the  buildings  as  well  as  under  the  streets,  caused 
trouble,  however,  and  during  the  spring  and  summer  of  1905 
settlements  of  streets  and  buildings  occurred,  with  the  result 
that  the  effect  of  city  tunnel  construction  upon  the  foundations 
of  buildings  was  made  the  subject  of  expert  investigation.  The 
Commissioner  of  Public  Works  appointed  a  committee  of  engi- 
neers to  investigate  the  cause,  and  their  first  report  stated  that 
no  settlements  had  occurred  where  the  main  tunnels  had  been 
built  under  air  pressure,  but  that  they  had  occurred  where  con- 
nections or  spurs  had  been  built  without  the  use  of  air  pressure. 
A  later  report  recorded  specific  instances  of  settlement  and 
showed  that  a  serious  problem  faced  the  tunnel  company.  The 
main  tunnels  are  built  in  the  Chicago  clay  and  at  a  depth  of 
about  20  feet  from  the  street  surface  to  the  crown  of  the  tunnel  ; 
as  they  are  located  under  the  center  lines  of  the  streets  they  are 
clear  of  the  lines  of  pressure  from  the  buildings,  and  are  subject 
only  to  the  pressure  due  to  the  overlying  material.  At  street 
intersections  the  tunnels  also  have  intersections,  and  the  two 
lines  of  straight  tunnel  are  in  many  cases  connected  by  four 
curved  tunnels,  as  already  explained.  This,  of  course,  involves, 
the  removal  of  a  great  mass  of  material,  and  unless  the  work  is. 


THE  CONSTRUCTION  OF  THE  SIMPLON  TUNNEL 

prosecuted  very  carefully  there  is  liable  to  be  a  slip  or  movement 
of  the  clay.  The  construction  of  one  of  these  intersections 
without  sufficient  care  and  precaution  is  given  as  the  cause  of 
one  of  the  street  settlements  already  referred  to. 

But  a  much  more  serious  matter  is  that  of  tunneling  through 
clay  subjected  to  pressure  from  neighboring  buildings.  As  long 
as  the  tunnels  were  to  be  used  simply  as  conduits  for  electric 
wires  and  cables,  there  would  be  very  little  of  this  class  of  work, 
but  when  their  use  for  transportation  purposes  was  planned  it 
was  proposed  to  build  lateral  branches  and  spurs  to  serve  post- 
offices,  newspapers  and  express  offices,  railway  passenger  and 
freight  stations,  wholesale  and  retail  stores,  warehouses,  office 
buildings,  etc.  These  spurs  would  enter  the  basements  of  modern 
buildings  having  deep  basements,  while  in  other  cases  they 
would  connect  with  shafts  having  elevators  to  serve  the  build- 
ing above.  The  construction  of  these  connections  must  involve 
the  excavation  of  clay  under  varying  degrees  of  pressure  from 
the  buildings,  and  when  any  void  is  left,  however  small  and  if 
only  temporary,  the  clay  will  fill  in  and  the  movement  of  the 
clay  body  may  extend  for  considerable  distances.  The  engi- 
neering committee  considered  that  the  tunnel  company  had  un- 
dertaken the  construction  of  these  branches  without  having 
given  sufficient  consideration  to  the  special  conditions  affecting 
this  phase  of  its  work,  and  recommended  that  no  more  such 
branches  should  be  built  until  the  special  conditions  in  each  par- 
ticular case  had  been  carefully  studied  and  a  proper  course  of 
construction  planned.  Whatever  care  is  taken,  however,  some 
settlement  is  considered  unavoidable.  The  use  of  compressed 
air  will  not  suffice  to  sustain  the  material,  and  in  fact  its  use 
in  this  part  of  the  work  was  not  considered  practicable  by  the 
committee.  The  soil  under  pressure  must  be  supported  by 
mechanical  means,  and  it  was  pointed  out  in  the  report  that  the 
case  "is  a  building  proposition,  and  the  methods  common  in 
building  practice  will  probably  meet  all  the  difficulties  that  may 
be  encountered."  The  committee  also  recommended  the  adop- 
tion of  a  circular  section  for  the  spurs  and  branches  instead  of 
the  horseshoe  section  of  the  main  tunnels. 


300  MODERN    TUNNEL    PRACTICE 

The  work  was  all  planned  by  Mr.  George  W.  Jackson,  Chief 
Engineer  and  General  Manager  of  the  Illinois  Tunnel  Con- 
struction Company,  and  has  been  executed  by  day  labor  under 
his  direct  supervision. 


APPENDIX 

GLOSSARY  OF  SOME  OF  THE  MORE  UNUSUAL  TERMS 
USED  IN  TUNNELING 

ADIT.— See  Heading. 

AIR-LOCK. — A  device  employed  in  connection  with  the  use  of  compressed 
air,  for  permitting  men  and  material  to  pass  from  the  normal  atmo- 
spheric pressure  to  a  higher  pressure,  or  the  reverse,  without  undue 
loss  of  pressure  in  the  working-chamber. 

AIR-SHAFT. — In  mining,  a  shaft  used  solely  for  ventilating  purposes. 

ALIGNMENT. — The  laying-out  of  the  axis  of  a  tunnel  by  instrumental  work. 
See  Ranging. 

ARCH-BLOCKS. — A  term  applied  to  the  wooden  voussoirs  used  in  framing 
a  timber  support  for  the  tunnel  roof,  when  driving  a  tunnel  on  the  co- 
called  American  system.  These  blocks  are  made  of  plank,  super- 
imposed in  three  or  more  layers  and  breaking  joint. 

BACKING. — The  rough  masonry  in  a  wall  faced  with  a  better  class  of  work. 

BACK-JOINT. — A  joint-plane  more  or  less  parallel  to  the  strike  of  the  rock- 
cleavage;  frequently  vertical. 

BALLISTIC  EFFECT. — The  throwing  of  rock  to  a  distance  from  the  exploded 
charge,  a  thing  to  be  avoided  in  rock-blasting. 

BARS. — Strong  timbers  placed  horizontally  for  supporting  the  poling- 
boards  in  the  face  of  the  excavation. 

BATTERY. — A  magneto-electric  apparatus  employed  in  firing  an  explosive 
connected  with  it  by  a  pair  of  insulated  copper  wires. 

BEARERS. — In  shaft-sinking,  heavy  sticks  of  timber,  longer  than  the  width 
of  the  shaft,  set  in  niches  cut  in  the  rock,  and  used  as  supports  for 
timber-sets. 

BEARING-IN  SHOTS. — Bore-holes  tending  to  meet  in  the  body  of  the  rock; 
intended  to  "unkey"  the  face  when  charged  and  fired. 

BENCH. — In  tunnel  excavation,  where  a  top-heading  is  driven,  the  bench 
is  the  mass  of  rock  left,  extending  from  about  the  spring-line  to  the 
bottom  of  the  tunnel. 

BENCH-MARK. — A  permanent  mark  of  a  suitable  character  for  preserving 
and  transferring  vertical  elevations  in  a  tunnel. 

BIT. — A  piece  of  steel  welded  to  the  end  of  a  drill,  or  the  point  of  a  pick. 
The  horizontal  section,  of  this  cutting  edge  is  either  +  or  x-shaped; 
the  edges  making  an  angle  of  nearly  90°. 

BLOCK-HOLING. — The  operation  of  drilling  and  blasting  a  detached  boulder 
or  mass  of  rock ;  the  purpose  being  to  reduce  the  mass  to  dimensions 
more  easily  handled  or  transported,  or  cut  for  building  purposes. 

BOWK. — An  English  term  fo-r  an  iron  tub  used  in  hoisting  debris  from  a 
shaft. 

BREAKERS. — The  row  of  drill-holes  above  the  mining  holes  in  a  tunnel  face. 

BREAST-BOARD. — The  timbers  or  boards  placed  horizontally  across  the  face 
of  an  excavation,  or  heading,  to  prevent  the  inflow  of  gravel  or  other 
loose  or  flowing  material. 

BROB. — An  English  term  for  a  wrought-iron  spike  driven  into  bars  and 
sills  to  steady  the  head  or  foot  of  a  prop. 

301 


302  APPENDIX 

BULKHEADS. — Masonry  diaphragms  built  across  a  subaqueous  tunnel  where 
compressed  air  is  used,  as  a  precaution  and  to  prevent  the  flooding  of 
an  entire  tunnel  in  case  of  an  accident.  These  bulkheads  are  usually 
kept  some  distance  in  the  rear  of  the  working  face,  and  are  provided 
with  two  air-locks;  one  of  them  is  an  emergency-lock  near  the  roof. 

BULL. — An  iron  rod  used  in  ramming  clay  to  line  a  shot-hole. 

BULLING. — Lining  a  shot-hole  with  clay. 

BURDEN. — In  blasting,  the  volume  of  rock  that  should  be  broken  by  a  proper 
charge  of  powder. 

CAGE. — The  elevator  used  in  a  shaft  for  hoisting  the  cars  loaded  with 
muck.  The  cage  is  generally  provided  with  a  safety  device  intended  to 
hold  the  cage  and  its  load  in  the  case  of  a  breaking  hoisting-rope. 

CENTERS. — Framed  supports,  usually  arch-shaped,  upon  which  are  placed 
the  lagging- boards  used,  in  building  an  arch,  for  supporting  the  roof  of 
a  tunnel. 

CHAMBER-BLASTING. — Used  in  very  heavy  blasting,  where  a  great  quantity 
of  rock  is  to  be  thrown  down  at  one  time  by  a  correspondingly  large 
charge.  A  tunnel  or  drift  is  usually  run  to  the  site  of  the  chamber, 
and  the  latter  is  excavated  and  charged.  The  drift  is  well  packed  with 
earth  and  sand  before  firing.  In  such  a  chamber  or  series  of  chambers 
as  much  as  7,000  Ibs.  of  dynamite  may  be  placed,  throwing  down  350,000 
tons  of  rock  at  one  blast. 

CHAMBERING.— The  enlargement  of  the  bottom  of  a  deep  drill-hole  by  the 
successive  explosion  of  small  charges.  The  purpose  is  to  provide  room 
for  a  final,  large  charge  of  powder  to  be  used  in  throwing  down  a 
large  mass  of  material. 

CHOG. — English  term  for  chocks,  or  blocks  spiked  into  the  corner  of  a 
shaft  to  form  a  bearing  for  the  side-waling  piece,  or  the  blocks  used  in 
headings  to  separate  the  cap  and  poling-board. 

CHURN-DRILL. — A  long  iron  bar  with  a  steel  cutting-edge,  used  in  quarrying 
or  in  blasting  hard-pan,  etc.  It  is  worked  by  lifting  and  letting  it  fall. 

COLLAR. — The  bar,  or  cross-piece,  in  a  framed  timber  set.  The  first  wood 
frame  in  a  shaft. 

COLUMN  or  BAR. — This  is  a  round  column  set  vertically  or  horizontally  in 
a  heading  and  to  it  the  machine-drill  is  clamped.  This  column  is  pro- 
vided with  a  head  at  one  end,  and  a  shoe  at  the  other  end  provided 
with  a  screV  for  setting  it  up  against  the  rock  walls.  A  column  gives 
a  firmer  support,  as  a  rule,  than  the  tripod  also  used  for  holding  the 
drill.  Blocks  of  tough  wood  are  placed  between  the  column  ends  and 
the  rock. 

CORE. — In  several  European  methods  of  tunneling,  the  sidewalls  are  built 
first  in  special  drifts :  and  the  arch  area  is  then  excavated  and  the  arch 
built,  leaving  the  central  mass  to  be  removed  last.  This  center  of  rock 
or  earth  is  called  the  "core." 

CRATER. — In  blasting,  the  funnel  of  rupture,  which  in  bad  rock  may  have 
very  steep  sides  and  a  relatively  small  volume  of  broken  rock. 

CRIBBING. — Close  timbering  in  lining  a  shaft.  A  structure  made  of  horizon- 
tal timbers  laid  one  on  top  of  the  other. 

CRIMPER. — A  tool  specially  made  for  fastening  a  cap  to  a  fuse. 

CROW-FOOT. — A  V-shaped  notch  in  an  arch-block;  sometimes  made  in  the 
bottom  block  where  this  rests  upon  the  wall-plate. 

CROWN-BARS. — Strong  timbers,  usually  round,  used  in  supporting  the  roof 
of  a  tunnel  in  the  English  method  of  driving. 

DOG. — A  round  iron  rod,  with  the  pointed  ends  bent  at  right  angles. 

DOLLY. — A  tool  used  to  sharpen  drills. 

DOWELS. — Round,  headless  iron  pins,  inserted  half  way  into  each  of  two 
abutting  timbers  to  prevent  slipping. 

DRAG-TWIST. — A  spiral  hook  used  for  wiping  a  blast-hole  with  hay  before 
charging  with  black  powder. 

DRAWING. — Removing  or  pulling  out  the  crown-bars  in  a  tunnel. 


APPENDIX  303 

DRIFT. — See  Heeding. 

DRIFT-FRAME. — See  Square  Sets. 

DUMP. — The  place  of  deposit  of  debris  from  an  excavation. 

ELECTRIC  FUSE. — A  metallic  cup,  usually  containing  fulminating  mercury, 
in  which  are  fixed  two  insulated  conducting  wires  held  by  a  plug,  the 
latter  holding  the  ends  of  the  wires  near  to  but  not  touching  each  other. 
At  this  plug  is  a  small  amount  of  a  sensitive  priming.  When  an  elec- 
tric current  is  sent  from  the  battery  through  these  conductors,  the  re- 
sulting spark  fires  the  priming,  then  the  fulminate  and  the  charge  of 
the  explosive  proper. 

ENLARGING  SHOTS. — Bore- holes  driven  after  the  face  of  the  rock  has  been 
"unkeyed,"  and  two  or  three  free-faces  have  thus  been  provided. 

FACE. — The  surface  exposed  by  excavation.  The  "working-face"  is  the 
face  at  the  end  of  a  heading,  or  the  end  of  a  full-size  tunnel  excavation. 

FALSE  SET. — A  temporary  set  of  timbers,  used  until  the  work  is  sufficiently 
advanced  to  put  the  permanent  set  in  place. 

FAULT. — A  dislocation  in  the  natural  strata. 

FLOAT. — This  is  a  timber  platform,  faced  with  boiler-iron  on  both  sides 
and  provided  with  rings  at  the  corners  for  lifting.  It  is  used  in  shaft- 
work  to  prevent  the  crushing  of  the  bottom  timbers  by  flying  frag- 
ments of  rock. 

FOOT  BLOCKS. — Flat  pieces  of  wood  placed  under  props,  to  give  a  broader 
base  and  distribute  the  weight. 

FOREPOLING. — The  act  of  driving  the  poling-boards  beyond  the  last  set  of 
timbers,  thus  forming  a  roof  for  further  advance. 

FREEZING-PROCESS. — A  method  invented  by  F.  A.  Poetsch  about  1883,  for 
penetrating  a  water-bearing  stratum.  Circulating  pipes  are  sunk  around 
the  site  of  a  shaft ;  and  the  ground  and  water  is  then  frozen  solid 
by  passing  thrqjugh  these  pipes  a  solution  of  brine.  The  frozen  material 
is  then  extavated  and  the  shaft  linetl  in  the  usual  manner. 

FUSE-CAP. — A  small  cylinder  of  copper,  closed  at  one  end  and  charged  with 
a  fulminate.  The  end  of  the  fuse  is  inserted  in  this  cap,  for  firing  a 
charge. 

GAD. — A  small  steel  wedge  used  for  loosening  seamy  rock. 

GALLERY. — A  drift  or  adit.  In  France  it  is  another  name  for  the  heading 
of  a  tunnel,  usually  called  "Advanced  Gallery." 

GALLOWS-FRAME. — The  frame  supporting  the  pulley  at  the  head  of  a  shaft, 
over  which  pulley  the  hoisting-rope  runs. 

CANISTER. — A  hard,  compact,  exceedingly  silicious  fire-clay. 

GRAIN. — As  applied  to  rock,  planes  of  cleavage  at  right  angles  to  the  rift, 
or  bed  of  the  rock. 

GUN. — A  term  applied  to  the  explosion  of  a  charge  in  a  bore-hole,  which 
simply  enlarges  the  hole  without  rending  or  splitting  the  rock. 

GUSSET. — A  V-shaped  cut  in  the  face  of  a  heading. 

HANG-FIRE. — A  term  applied  to  a  charge  which  is  delayed  in  exploding, 
but  does  eventually  explode. 

HEAD. — As  applied  to  rock,  natural  planes  of  cleavage  at  right  angles  to 
the  grain  and  the  rift  of  the  rock. 

HEAD-HOUSE. — A  covered  timber  framing  at  the  top  of  a  shaft,  into  which 
the  shaft-guides  are  continued  that  carry  the  cage  or  elevator.  The 
term  is  sometimes  applied  to  the  structure  containing  the  hoisting  en- 
gine, boilers  and  other  machinery,  in  addition  to  the  actual  hoisting- 
cage,  etc. 

HEADING. — A  smaller  excavation  driven  in  advance  of  the  full-size  section ; 
it  may  also  be  driven  laterally,  and  is  then  called  a  "Cross  Heading" 
or  "Side  Drift."  A  heading  may  be  driven  at  the  top  or  the  bottom  of 
the  full-size  face;  it  is  then  a  "Top"  or  a  "Bottom  Heading,"  as  the 
case  may  be. 

HEAD-PILES. — The  top  poling-boards  in  a  heading. 

HEAD-TREE. — The  cap-piece  of  a  heading-set. 


304  APPENDIX 

HEEL-OF-A-SHOT. — In  blasting,  the  face  of  a  shot  farthest  away  from  the 

charge. 
HITCH.— A  step  cut  in  the  side  of  a  shaft,  or  in  other  excavations,  for 

holding  timbers  for  various  purposes. 
HOLING-THROUGH. — Connecting  two  sections  of  a  tunnel  driven  toward  each 

other. 

HORSE-HEAD. — English  term  for  a  heading-frame,  of  a  cap  and  two  posts. 
INVERT. — A  flat  inverted  arch  of  masonry  used  for  the  floor  of  the  tunnel 

lining. 
JUMPER. — A  long  iron  drill,  with  a  steel  cutting-edge,   worked  by  blows 

from  a  heavy  hammer. 
KEY. — Of  an  arch;   the  top  closing-voussoir,   or   ring-stone.     The  "Key" 

may  also  be  a  closing  section  of  brick  masonry. 
KICKING-PIECES. — Short  struts    to   prevent   a   sill    or   other    member    from 

being  pushed  out  of  place. 
LAGGING. — Narrow  boards,   generally   planed,    placed   horizontally  on   the 

arch-frames  of  a  center.    On  this  lagging  the  arch  of  masonry  is  built. 

The  term  is  also  applied  to  poling-boards. 

LEAD-WIRES. — Two  insulated  copper  wires  leading  from  the  battery  or  ig- 
niting apparatus  to  the  primer-cartridge  in  an  explosive  charge.    These 

are  also  called  "Connecting  Wires." 
LINE  OF  LEAST  RESISTANCE. — As  this  term  is  used  in  blasting  operations.. 

it  indicates  the  shortest  line  that  can  be  drawn  from  the  charge  in  the 

bore-hole  to  the  outer  face  of  the  rock. 
LINING. — The  lining  of  a  tunnel  may  be  stone,  brick  or  concrete  masonry, 

iron  or  steel  rings,  or  concrete-steel.     In  the  early  American  tunnels 

wood  was  also  used  for  this  purpose. 
LOOP  TUNNEL. — A  method  of  gaining  grade  in  a  tunnel  location  by  looping 

or  folding  the  line  back  upon  itself. 

MINERS. — The  row  of  drill-holes  in  a  tunnel  face,  located  below  the  break- 
ing-down holes. 
MISS-FIRE. — A  term  applied  to  a  charge  which  from  some  cause  has  failed 

to  explode. 
MOP. — A  disc  of  some  material  used  around  a  drill,  to  prevent  water  from 

splashing  up. 

MUCK. — The  broken  rock  or  other  material  coming  from  a  tunnel  exca- 
vation. 
MUD-CAPPING. — A  method  of  breaking  up  boulders  by  placing  dynamite  on 

top  of  the  boulder  and  covering  this  with  wet  clay.    The  process  is  very 

wasteful  of  powder,  as  the  powder  does  not  do  its  best  work. 
NEEDLES. — An  English  term  used  for  a  special  form  of  poling-boards ;  they 

are  sometimes  made  of  iron  or  steel  plate  and  may  be  as  much  as  m 

feet  long  by  6  inches  wide. 

NIPPER. — A  name  given  to  the  boy  who  carries  the  drills  to  the  smithshop. 
OUT-CROPPINGS. — Applied  to  a  rock  or  ore-vein  as  seen  exposed  on  the 

surface. 
OVERWINDING. — A  term  applied  to  a  continued  pull  on  the  hoisting  rope  of 

a  cage,  after  the  cage  has  reached  the  top  of  the  shaft.  The  result  of 

this  carelessness,  or  accident,  is  a  broken  hoisting  rope  and   all   the 

danger  that  implies. 
PACKING. — Any  material,  usually  rock,  packed  between  the  rock-roof  of  a 

tunnel  and  the  top  of  the  arch-masonry. 
PIGEON-HOLE. — An  opening  left  at  the  meeting  of  two  sections  of  arch 

work,  permitting  the  workmen  to  close  the  arch  and  to  come  out.    The 

"Pigeon-hole"  itself  is  closed  from  below. 
PILOT-TUNNEL. — See  detailed  description  in  text. 
PLANT. — A  term  used  to  include  the  machinery,  derricks,  railway,  cars, 

etc.,  employed  in  tunnel  work. 
PLUG-AND-FEATHER  HOLE. — A  hole  drilled  for  the  purpose  of  splitting  a 

block  of  stone.    These  holes  are  usually  in  rows.   The  plug  is  a  slightly 


APPENDIX  305 

wedge-shaped  piece  of  iron  driven  between  two>  L-shaped  irons,  or 
"feathers,"  inserted  in  the  hole. 

PLUGS. — Small  wooden  pins  driven  into  holes  driven  in  the  rock-roof  of  a 
tunnel.  The  axis  of  the  tunnel  is  marked  on  these  plugs  by  tacks,  or 
by  small  iron  hooks  from  which  a  plummet-lamp  may  be  suspended 
for  sighting  upon. 

PLUMB-POSTS. — The  vertical  posts  at  the  side  of  a  tunnel,  resting  on  sills 
and  carrying  the  wall-plates ;  the  whole  supporting  the  tunnel  roof  by 
means  of  centering. 

POLING-BOARDS. — Narrow  boards  of  varying  lengths,  sharpened  at  the  front 
end  and  driven  forward  over  the  bars  to  support  the  roof  or  sides  of  a 
heading  or  of  a  full  arch  section. 

POP-SHOT. — In  blasting,  when  the  explosion  of  the  charge  simply  blows 
out  the  tamping. 

PORTALS. — The  entrance  and  exit  of  a  finished  tunnel,  usually  faced  by 
masonry  to  support  the  loose  rock  or  earth. 

PRIMER-CARTRIDGE. — The  cartridge  to  which  the  cap  and  fuse  are  attached, 
or,  in  electric  firing,  into  which  the  electric  cap  is  inserted. 

PROPS. — Struts  or  posts,  either  vertical  or  raking,  used  as  supports  or  stays 
in  tunnel  timbering.  The  inclined  prop  is  usually  called  a  "Raker." 

PUNCHEONS. — English  term  for  the  props,  or  posts  set  up  between  lines 
of  waling  in  shaft-sinking.  See  Studdle. 

RAKER. — See  Props. 

RANGING. — The  English  term  for  aligning  a  tunnel. 

RIFLED. — A  term  applied  to  the  three-cornered  section  of  a  hole  drilled 
by  hand.  Though  the  bit  is  supposed  to  be  turned  one-eighth  after 
each  blow,  to  insure  a  circular  hole,  the  majority  of  hand-drilled  holes 
are  three-cornered. 

RIFT. — In  sedimentary  rocks,  the  horizontal  plane  of  stratification,  or  the 
bed  of  the  rock. 

RUN. — The  escape  of  any  flowing  material  into  the  tunnel-area;  it  may  be 
sand,  gravel,  or  mud. 

RUNNERS. — English  term  for  sheet-piling. 

SAFETY  FUSE. — The  safety  or  time  fuse  is  made  of  a  core  of  meal-powder 
lightly  compressed  and  enclosed  in  one  or  more  wrappers  of  spun-yarn 
made  waterproof.  According  to  the  number  of  wrappers  and  the 
dampness  of  the  ground  in  which  they  are  to  be  used,  fuses  are  called 
"Single  Tape,"  "Double  Tape,"  etc. 

SCRAG. — The  batir  of  a  post. 

SERIES  SHOTS. — A  number  of  loaded  holes  connected  and  fired  one  after  the 
other.  In  contradistinction  to  "Simultaneous  Firing,"  where  the 
charges  are  connected  electrically,  and  are  all  exploded  at  one  time. 

SETTINGS. — The  timber  frames  used  at  intervals  in  shaft-sinking,  and  close- 
poled  behind. 

SHAFT. — Temporary  or  permanent  pits  sunk  to  give  access  to  an  under- 
ground working.  The  shaft  may  be  vertical  or  inclined,  though  the 
latter  is  only  used  in  mining  operations. 

SHIELD. — A  metal  diaphragm  used  in  tunneling  under  rivers,  or  in  water- 
bearing or  loose  material  under  cities.  The  shield  may  be  cylindrical 
and  include  the  entire  tunnel  section ;  or  it  may  be  a  "Roof-shield" 
and  support  the  roof  only. 

SHIFT. — The  working  hours  per  day  of  a  gang  of  laborers. 

SIDE-PILES. — Another  term  for  the  side  poling-boards  in  driving  a  heading. 

SIDE-TREES. — The  two  posts  of  a  heading-set. 

SILLS. — Strong  timbers  laid  horizontally  to  support  posts  or  other  tunnel 
timbers. 

SKIPS.— Metal  buckets,  usually  opening  at  the  bottom ;  sometimes  used  for 
removing  water  from  shafts. 

SLIP. — A  fault.     A  smooth  joint  where  one  stratum  has  moved  on  another. 

SOCKET. — The  bottom  of  a  shot-hole,  not  blown  away  in  firing. 


306  APPENDIX 

SOLDIER-FRAME. — Frames  set  into  the  inside  of  a  shaft  prior  to  breaking 

through  for  a  heading. 
SOLE-PLATE. — Formed  of  several  pieces  of  lagging  fastened  together,  and 

laid  down  in  the  bottom  of  an  invert.     It  forms  a  base  for  the  iron 

ribs  used  in  laying  a  concrete  invert. 

SPIRAL  TUNNEL. — A  method  of  gaining  grades  in  a  tunnel  by  driving  the 
tunnel  on  a  constantly  ascending  and  circular  line. 

SPOON. — A  scraper,  or  similar  instrument,  for  cleaning  the  sludge  out  of 
shallow  drill-holes.  This  spoon  is  usually  made  of  one-fourth  to  one- 
half  inch  iron  rod,  with  a  disc  at  each  end. 

SPRAG. — The  horizontal  member  of  a  square  set  of  timbers  running  parallel 
to  the  axis  of  a  heading. 

SPRINGING  A  HOLE. — Enlarging  a  drill-hole  at  the  bottom  to  permit  the 
use  of  a  greater  charge  of  explosive.  This  is  usually  done  by  ex- 
ploding smaller  charges  of  dynamite  at  the  bottom  of  the  hole  and  thus 
pulverizing  the  harder  rock.  The  process  is  also  called  "chambering," 
"shaking,"  and  "bullying." 

SPRINGING-LINE. — The  horizontal  line  drawn  at  the  point  of  origin  of  an 
arch ;  or  at  the  point  where  the  intrados  of  the  arch  meets  the  interior 
face  of  the  side-walls  or  abutments. 

SQUARE  SETS. — Timber  frames  used  at  intervals  to  support  poling-boards, 
in  shaft-sinking  or  driving  a  heading. 

STATIONS. — Points  on  the  center-line  of  a  tunnel,  permanently  marked. 
These  stations  may  be  outside  of  the  tunnel  and  used  for  projecting  the 
center-line  into  the  tunnel,  or  they  may  mark  the  center-line  inside  the 
tunnel. 

STONE-BOAT. — A  species  of  wooden  sled,  used  for  hauling  large  stones  a 
comparatively  short  distance. 

STRETCHERS. — In  shaft-sinking,  the  cross-pieces  holding  the  waling  apart. 

STRIKING. — Lowering  the  arch-centers,  after  the  masonry  is  completed 
and  the  mortar  set. 

STRIKING-PLATES. — Two  horizontal  timbers  separated  by  striking-wedges 
and  supporting  an  arch-center.  The  latter  is  lowered  by  slacking  the 
wedges. 

STRIPPING. — Removing  the  earth,  etc.,  overlying  rock  that  is  to  be  exca- 
vated. English  miners  apply  the  term  of  "over-burden"  to  this  same 
overlying  material. 

STUDDLE. — A  square  timber,  or  short  post,  placed  vertically  between  two 
sets  of  shaft  timbers. 

STUMP-PROP. — Short  posts  set  under  the  crown-bars  of  a  tunnel. 

SUMP. — An  excavation,  usually  at  the  bottom  of  a  shaft,  to  collect  water 
so  that  it  may  be  better  handled  by  the  pumps  or  buckets. 

TAILING. — Giving  the  proper  angle,  or  elevation,  in  driving  the  poling- 
boards  in  a  heading. 

TAMPING. — The  material  placed  over  a  charge  in  a  bore-hole,  to  better 
confine  the  force  of  the  explosion  to  the  lower  part  of  the  hole. 

TENDING  CHUCK. — Pouring  water  into  a  drill-hole  to  assist  in  drilling. 

TEMPLATE. — A  form  for  building  tunnel  inverts. 

TIMBERING. — A  general  term  for  the  placing  of  timber,  to  support  the  roof 
or  the  face  of  a  tunnel  during  excavation  and  lining. 

TOOTHING. — In  a  stone  or  brick  arch,  the  jogs  left  in  the  face  of  the  arch- 
work,  for  the  purpose  of  joining  it  to  the  following  section. 

TRIMMERS. — The  top  row  of  holes  in  a  tunnel  face. 

TUCKING  SPACE. — The  space  between  the  blocks  separating  the  cap  in  a 
heading-set  from  the  poling  driven.  This  space  provides  for  driving 
the  second  set  of  poling-boards. 

UNKEYING.— In  attacking  a  rock-face  the  first  effort  of  the  miner  is  di- 
rected toward  making  a  cut  that  will  permit  the  succeeding  shots  to 
exert  the  greatest  force  with  the  minimum  charge  of  explosive.  In  do- 


APPENDIX  307 

ing  this  "unkeying,"  he  takes  advantage  of  any  persistent  seam  in  the 
rock  face. 

WALINGS. — Sets  of  longitudinal  timbers  used  as  guides  in  driving  sheet  pil- 
ing, etc.  Also  the  horizontal  side-pieces  in  a  shaft-set  separated  by 
"stretchers." 

WALL-PLATE. — A  horizontal  timber  supported  by  posts  resting  on  "sills" 
and  extending  lengthwise  on  each  side  of  the  tunnel.  On  these  wail- 
plates  the  roof-supports  rest. 


INDEX  TO  CONTENTS 


PAGE 

AIR-LOCKS — Their  purpose 213 

Kiel  dry-dock 231 

The  Hughes 223 

Hyde   Park  tunnel 225 

Morison's  228 

The  O'Rourke 218 

Victoria  Bridge 230 

Zschokke-Terrier 222 

AIR-REFRIGERATION  in  tunnels..  212 
In  Simplon  tunnel 260 

Air-valve — Slow  pressure 232 

ALIGNMENT  of  tunnels 6.4 

Transfer  of  line  into   Cin- 
cinnati     Water      Works 

tunnel    291 

Dunham  method  of 6 

Simplon  tunnel 269 

ARCH-CENTERS  —  Requirement 

and  form  of 99 

Adjustable   101 

Cincinnati     and     Southern 

R.   R ioo 

Norfolk  and  Western  R.  R.  101 
Steel— East  Boston  tunnel.   109 

Battery — Electric   firing 25 

BLASTING — General      principles 

of   34 

Nomenclature  36 

Square  center  cut 37 

V-shaped  center  cut 38 

Qualities  of  rock,  testing.  .  41 
Methods   on   N.   Y.    Rapid 

Transit  tunnel 39 

To     prevent     crushing     of 

shaft-timbers  by 45 

BORE-HOLES  —  Diameter       and 

length  of 36 

Location  of 37 

Brant  Rotary  Drill  at  Simplon 

tunnel    272 

Brick-crates  —  New       Orleans 

drainage  184 

Cement  mortar  car — Mullan 

tunnel  179 

COMPRESSED  AIR — Effect  of,  on 

human  organism 216 


PAGE 

Hospital-lock    216 

Human  endurance  under. .  214 

Limits  of  working  in 215 

CONCRETE  TUNNEL  LINING 107 

Cascade  tunnel 173 

East  Boston  tunnel 160 

N.  Y.   C.  &H.  R.  R.  R....  193 
Concrete     invert     form — sewer 

tunnel    in 

Concrete  side  walls — building. .   180 
Concrete  and  steel  lining,  East 

Boston  tunnel 119 

COST — Concrete  tunnel  lining.  .   193  „ 
Diamond  drill  work,  Africa  199 
Diamond  drill  work,  Mon- 
tana    200 

Drifting  and  cross-cutting.   188 
Driving    heading    in     Me- 

lones    Mine 190 

Excavation,  timbering  and 
packing  Little  Tom  tun- 
nel   77 

Hand-drilling     at     Golden 

Eagle   Mine 186 

Hand-work    in    W.    Va.    & 

P.  R.  R.  tunnel 189 

Mass.    Pipe   Line   Gas   Co. 

tunnel    143 

Mine      hauling     by     com- 
pressed air  vs.  mules.  . .  .   198 
O.  R.,  P.  C.  &  W.  R.  R. 

tunnel    191 

Power      drilling,      Lincoln 

Gold  Mine 187 

Square-set  timbering 197- 

Steam-shovel  work 192- 

Water-hoisting  vs.  pump- 
ing in  mines 195 

Crown-bars,  made  of  old  rails. .     86 
Crown-bars — Special  iron 85 

Distance  targets — Hoosac 12 

Drifting  and  cross-cutting 188 

Dry-sand  tunneling 94 

Dumping  wagon — The  Shadbolt  178 
Dunham      method      of     tunnel 

alignment 6 


309 


310 


INDEX    TO    CONTENTS 


PAGE 

DYNAMITE — Frozen 28 

Loading  with 43 

Thawing-house 30 

ELECTRIC — Firing  24 

Firing  apparatus 25 

Power — heat  from,  in  sub- 
ways        203 

EXPLOSIVES — Atlas  powder 20 

Consumption  of 39 

Dynamite  18 

Forcite 19 

Gunpowder   14 

Handling  and  storing 27 

Hellhoff  ite 22 

Hercules  powder 20 

Joveite 20 

Judson  powder 20 

Lithof  racteur 19 

Nitrogelatine  —  Composi- 
tion and  use 18 

Nitroglycerine — Its  compo- 
sition, power,  expansion, 

etc 16 

Effect  of  fumes 44 

Oxonite 22 

Plancastite  22 

Power  of,  bulk  for  bulk. . .  19 

Rack-a-rock 22 

Romite    22 

Used  in  Simplon  tunnel...  274 

Sprengel  class  of 21 

Excavation — Sequence  of  ope- 
ration, Simplon  tunnel. 
(See  also  tunnel  timber- 
ing)   270 

Expansion  joint  in  tunnel  lin- 
ing    137 

FORCE  of  gunpowder 15 

Of  nitroglycerine 16 

FREEZING  process  in  shaft-sink- 
ing, history  of 236 

As  applied  at  Iron  Moun- 
tain   238 

At  Ronnenberg,  Germany.  237 
Frozen  Soil — Conductivity  of. .  238 

FUSE — Electric 24 

Safety  or  time 23 

Geology  in  tunnel  location 2 

Grouting  sub-aqueous  tunnel . .  142 

GUNPOWDER — Composition,    etc.  14 

Loading  with 82 

Hamilton  Powder  Co.  dyna- 
mite thawer 29 

Hand-auger  for  prospecting 

work  244 


PAGE 

Hand-drilling— Cost  of  at  Gol- 
den Eagle  Mine 186 

Heading  timbering,  Simplon 

tunnel  282 

High  explosives — Precautions 

in  firing 26 

Hoisting  cage — Simple  form  of    52 

Hoisting  hook,  Walker  detach- 
able    181 

Humidity  in  subways 206 

Illumination  in  Simplon  tunnel  261 

Lamps  for  sighting  in  tunnels. .     13 
Line  of  least  resistance  in  blast- 
ing       34 

LINING   for   heavy  pressures — 

Simplon  tunnel 279 

Timber      in      sub-aqueous 

tunnel,  Boston 140 

Location  of  tunnels I 

Loose  gravel,  driving  through.     78 

Magazine,  powder,  design  of . .     31 

NEEDLES — Iron  85 

As  used  on  N.  Y.  subway.   168 

Open-cut  work,  N.  Y.  subway.  165 

Pilot-piles,  Harlem  river  tunnel  127 

Pilot-tunnel  system 91 

PLANT — Brick  crates,  New  Or- 
leans drainage 184 

At  Cascade  tunnel 171 

Concrete-mixing,  New  Or- 
leans     ' 183 

Detaching  cage-hook 181 

Dump-car,     New     Orleans 

drainage   182 

Scraper   loading 176 

Simplon   tunnel 252 

Steam-shovel    work    inside 
tunnel,   N.    Y.   &   H.    R. 

R.   R 180 

(See  Ventilation.) 

Plummet  lamps 249 

Powder  magazine,  plan  of 31 

POWER  DRILLING,  cost  of  at  Lin- 
coln Mine 187 

Hints  on 45 

Power      installation,      Simplon 

tunnel    253 

Power  plant,  Cascade  tunnel. .   174 

Primer  cartridge-making 23 

Prospecting  work,  tools  for. . . .  244 

QUICKSAND — Definition  of 239 

Sewer  tunnel  in 93 

Shaft-sinking    in 57 


INDEX    TO    CONTENTS 


PAGE 

Rock  temperatures  in  tunnels. .  239 

Rollers  under  arch-centers....  102 

ROOF-SHIELD,  Boston  subway...  157 

Metropolitan      Railway 

Paris 149,  ISO 

Orleans  Railway,  Paris....  146 

(See  Shields.) 

Scraper     loading     at     Kellogg 

tunnel    176 

Screw   piles,    used   under   sub- 
aqueous  tunnel 137 

SHAFT — Automatic  dump  for. .  177 
O'Rourke    system    of   con- 
struction    218 

Location     and     dimensions 

of 47 

A    sheet-piling 62 

Built   with  segmental  tim- 
bers     140 

Simple  head-house  for....  51 
Stopping  flow  of  water  at 

bottom  of 60 

Transferring     center     line 

down 10,  288 

Framing,  Norway,  Mich. . . 

Aspen  tunnel » . 

Shaft-house,  a  steel 54 

SHAFT      SINKING,      controlling 

features  of 48 

Cost    of   at    Golden    Eagle 

Mine   186 

At  Lincoln  Gold  Mine,  cost 

of  187 

In   wet  gravel   and   quick- 
sand    57 

SHEET-PILING — Driving  of 63 

As  used  at  Harlem  tunnel.  127 

SHIELDS — Tunnel,  history  of...  113 

Blackwell  tunnel 114 

East  Boston  tunnel 121 

East  River  gas  tunnel 123 

Mass.  Pipe  Line  Gas  Co. . .  142 

Orleans  Railway,  Paris 146 

St.  Clair  tunnel 116 

Friction    on,    at    St.    Clair 

tunnel 118 

Screw-jack  type 138 

The   Shankland 139 

Spree  tunnel,  Berlin 118 

Steel  traveling no 

Siphon  tunnel,  Mass.  Pipe  Line 

Gas  Co 142 

Skips,  for  shaft  work 57 

Snow  fall,  in  tunnel  location. . .  8 
Soap    and    alum    solution    for 

waterproofing  concrete. .  242 

Station  points,  preserving 5 

Station  towers 9 


PAGE 

Steam-shovel  work,  cost  data. .  192 
SUBWAY  —  Requirements      and 

location  144 

Atlantic  Avenue,  Brooklyn.  168 

Boston  system 154 

Buda-Pest   163 

East  Boston 159 

Humidity  in 206 

Orleans  Railway,  Paris....   145 
N.  Y.  Rapid  Transit,  gen- 
eral plan  of 163 

Open-cut  work  on 165 

SURVEY  WORK — Cascade  tunnel      9 

Cincinnati  W.  W.  tunnel..  289 

Switchback — Cascade  tunnel ...      8 

Tamping,  necessity  of 27 

Temperatures     in     deep     tun- 
nels   211,  239 

Thawing  dynamite 29 

TRANSPORTATION     in     Kellogg 

tunnel    177 

In  Simplon  tunnel 265 

Traveler — N.  Y.  subway  lining.  107 

(See  Arch-Centers.) 
TUNNEL — Aspen,  shaft  lining. .     64 

Boulder 102 

Cascade 8 

Cincinnati  Southern  R.  R.  100 
Cincinnati  Water  Works..  285 
Cross-section  instruments..  247 

Crow's  Nest  Pass 78 

Debris,  handling  in 173 

East  Boston 109,  159 

Hoosac    shafts 12 

Kellogg,  scraper — loading  at  176 

King's  Cross,  London 85 

Lake  View,  Chicago 81 

Location  of i 

Meudon,  France 87 

Moncreiffe,  England no 

Mullan,  relining 179 

Musconetcong,    relining 104 

Norfolk  &  Western  R.  R. .  101 
O.  R.,  P.  C.  &  W.  R.  R., 

cost   data 191 

Pracchia,  ventilation  of. ...  204 

Relining  102 

Revere  Beach,  Mass 95 

Sand  tunnel  in  Brooklyn. .     82 
Simplon,    detailed   descrip- 
tion of 250 

Simplon,  standard  sections  267 

Steel-lined  86 

Surveying  of 4 

Telephone   and   freight,   in 

Chicago 293 

W.  Va.  &  P.  R.  R.  R.,  cost 
data 189 


312 


INDEX    TO    CONTENTS 


PAGE 

TUNNEL  LINING,   cement   mor- 
tar car  for 179 

Simplon   tunnel 278 

TUNNEL      TIMBERING — General 

principles  of 65 

American  system 74 

Austrian    system 72 

Belgian  system. 69 

Belgian-German   system. . .  69 

English- American  system..  67 

German   system 71 

Hoosac   69 

Little  Tom 77 

Musconetcong 68 

N.  Y.  subway 106 

Ozernitz  73 

St.   Cloud 70 

Simplon   tunnel 276 

Triebitz 72 

TUNNELING — Under  clay  pres- 
sure     298 

Crutch   system 81 

In  dry  sand 82 

Through  dry,  running  sand  94 

East  Boston 161 

Iron  crown-bar  system.  ...  85 

In  loose  gravel 78 

Meem  poling-board  system  84 

With-  pilot-tunnel 91 

Sand-chamber  and  caisson 

method   87 

With  screw-pile  supporting 

column 134 

Sewer     tunnel      in      sand, 

Chatham  Square,  N.  Y. .  97 

Simplon    tunnel 280 

In  soft  ground,  East  Bos- 
ton    159 

Through  soft  ground 95 

Tunneling    terms — (See    Glos- 
sary in  Appendix.) 
TUNNELS,  SUBAQUEOUS — Black- 
well,  London 114 

Cast-iron 123,  134 


PAGE 

East  Boston 119 

East  River  Gas 123 

Harlem  River 125 

McBean  system  of 125 

Mass.  Pipe  Line  Gas  Co...  140 

Pa.  R.  R.,  Hudson  River. .  134 

St.  Clair 116 

Spree,   Berlin 118 

VENTILATION      IN     TUNNELS — 

General  principles  of....  201 
Volume    of    fresh    air    re- 
quired,  formula  for 202 

Baltimore      and      Potomac 

tunnel    207 

Boston  subway 154,  205 

Cascade  tunnel 174 

East  Boston  tunnel 206 

Mersey   tunnel 208 

Pennsylvania  Avenue  sub- 
way, Philadelphia 209 

Saccardo  system 204 

Simplon   tunnel 210,  257 

Required      in      electrically 

operated   subways 203 

Vernier   scale,   for  transferring 

line  down  shaft 12 

WATERPROOFING — Concrete  ex- 
periments upon 240 

Concrete  tunnel  lining 244 

With  asphalt 243 

With  linseed  oil 243 

Atlantic  Avenue  subway..  .  169 

Subway,   Buda-Pest 163 

Water-hoisting  vs.  pumping  in 

mines,  cost  data 195 

Water-hoist,  electric 196 

Wet  gravel,  shaft-sinking  in...  57 

Wires,   connecting. 25 

Appendix — Glossary  of  some  of 
the  more  unusual  terms 
used  in  tunneling 103 


INDEX  TO   ILLUSTRATIONS 


PAGE 

AIR-LOCK,  Hughes 224 

Hyde  Park  tunnel 224 

Kiel  dry-dock  for  workmen  231 
Kiel  dry-dock  for  materials  233 

Morison  229 

O'Rourke 219 

Victoria  Bridge 230 

Zschokke-Terrier 221 

Air-valve,  pressure  regulating.  232 

Blasting  nomenclature,  diagram     56 
BLASTING — Square  center-cut. .     37 

V-shaped   center-cut 38 

Methods  N.  Y.  subway....     41 
Brick,  crates  for  handling 184 

Caisson,  O'Rourke  wooden....  217 

Caissons  used  at  Meudon  tun- 
nel      90 

Cast-iron     lining     rings,     East 

River  gas  tunnel 123 

Cement     mortar     car,     Mullan 

tunnel    179 

Concrete  invert,  form  of in 

CONCRETE  LINING,  Boston  sub- 
way     ". 119 

Peekskill  tunnel 194 

Concrete  mixers,  New  Orleans 

drainage   works 182 

Crown-bars  made  of  old  rails. .     86 

Dump-car,  New  Orleans  drain- 
age     182 

Dumping  wagon,  the  Shadbolt.   178 

Dynamite  thawer 29 

Dynamite-thawing  house 31 

Hoisting  cage  and  head  house.     51 
Hoist-hook,  detaching 181 

McBean  sub-aqueous  tunnel...   129 
Mold  for  side-walls,  N.  Y.  sub- 
way       109 

Pilot-tunnel  system 92 

Plant,  arrangement  of,  on  New 

Orleans  drainage  works.   183 
Plummet  lamp 248 

Quicksand,  sewer  tunnel  in 93 

Sand,  sewer  tunnel  in 97 


PAGE 

Sand-chamber  and  caisson  sys- 
tem       88 

Scraper-loading  device  in  Kel- 
logg tunnel 175 

SHAFT-FRAMING,       longitudinal 

section 60 

Connection    with    rock    at 

bottom 61 

Top  and  bottom  sets 59 

Shaft-lining,  Aspen  tunnel 64 

Shaft-dump,  automatic 177 

Sheet-piling  shaft,   N.   Y.   sub- 
way        62 

SHEET-PILING,     Harlem     River 

tunnel    127 

Device  for  cushioning  blow 

on  63 

SHIELD,  Blackwell  tunnel 115 

Boston  subway.  ......  .121,  158 

East  River  gas  tunnel 123 

Mass.  Pipe  Line  Gas  Co. . .   143 
Metropolitan      Railway, 

Paris 15! 

Orleans  Railway,  Paris 147 

St.  Clair  tunnel 117 

Screw-jack  type 139 

Shankland's  140 

Spree  tunnel,  Berlin 118 

SIMPLON      TUNNEL — Map      of 

routes    251 

Profile  252 

Air  circulation  in 259 

Brandt  rotary  drill 271 

Brandt  rotary,  mounted...  272 

Extra  heavy  lining 279 

Cross-galleries    268 

I-beam  and  timber  frames.  281 

Lining   construction 278 

Progressive  stages  in  tim- 
bering     277 

Refuge  chambers 269 

Sequence  of  excavation 270 

Sequence    of    timbering    in 

soft   rock 282,  283 

Standard  sections 267 

Standard   timbering 276 

Suggested    arch    construc- 
tion    284 


313 


INDEX  TO  ILLUSTRATIONS 


PAGE 

SIMPLON  TUNNEL— 

Ventilating    plant,     Italian 

end  258 

Ventilating     plant,     Swiss 

end  257 

Skips  and  cages 56,    57 

STEEL  SHAFTHOUSE,  elevation..     55 

Plan 54 

SUBWAY — Boston,  in  concrete 

and  brickwork, 157 

Boston,     general     plan     in 

steel   155 

Boston,     Atlantic     Avenue 

station  159 

Detail  of  building  side- 
walls  160 

Detail  of  building  arch.  161 

Buda-Pest,  section 162 

New    York,    in    steel    ai.d 

concrete    164 

New  York,  earth  and  reck 

sections  165 

New  York,  methcd  of  ex- 
cavating,   east    of    Fifth 

Avenue 166 

New  York,  method  of  ex- 
cavating   between    Fifth 

and  Sixth  Avenues 167 

Atlantic  Avenue,  Brooklyn  169 

Tunnel      alignment,      Dunham 

method   I 

TUNNEL,  Cascade,  map  of 8 

Excavating   and   lining 

plant  of 172 

Cincinnati     Water    Works 

section  286 

East  end  shaft 289 

Cross-sectioning   device...  247 
Tunnel    driving,    various    sys- 
tems of 66 

Harlem    River,    twin  sec- 
tion    124 

Working    platform, 

guide  frames,  etc 126 

Harlem     River,     plan     for 
connecting  two  systems..  133 


PAGE: 

TUNNEL — 

P.  C.  &  W.  R.  R.  standard 

section IQ1 

Pennsylvania  R.  R.,   Hud- 
son River  cross-section..   135 
Details     of     bore-seg- 
ments     136 

Screw-pile     shaft     fit- 
tings     137 

Expansion     joint     for 

lining .' I3& 

TUNNEL       CENTERS  —  Boulder 

tunnel    103. 

Cincinnati  Southern  R.  R. 

standard  plan ioo> 

Musconetcong  tunnel 105 

New  York  subway 108 

Norfolk  &  Western  R.  R. .   101 
Set-screw  and  rollers  under  102 
Steel,  East  Boston  tunnel. .   109- 
TIMBERING — American    system, 

Little  Tom  tunnel 77 

Austrian  system 75 

Belgian  system 71 

Brooklyn  sand  tunnel 82 

Crow's  Nest  Pass  tunnel. .     78 

Crutch  system 81 

Hoosac  tunnel 60^ 

Iron  crown-bar  system....     84 

Musconetcong  tunnel 68 

Meem  system 83; 

Needles  used  in  Meem  sys- 
tem       85 

N.  Y.  subway 106 

Ozernitz  tunnel 73 

Revere  Beach  tunnel 94,    95 

St.  Cloud  tunnel 70 

Triebitz  tunnel 72 

VENTILATING     SYSTEM,     Balti- 
more and  Potomac  R.  R. 

tunnel,  Baltimore 20& 

Boston  subway 156,  205 

Mersey  tunnel 209 

Pennsylvania  Avenue  sub- 
way, Philadelphia 210 

Saccardo  system  of 204 

Vernier  scale   for  transferring 

line  down  shaft 12 


12 


IS  DUE  ON  THE 
STAMPED  BELOW 


DATE 


VD  02 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


